CHICAGO — Restaurant operators are refreshing salad menus with new proteins and trendy toppings. Not just the garden varieties here.

“Operators are definitely paying closer attention to salads, using bolder flavors, more detailed preparation methods and including more ethnic flavors,” said Eli Rosenberg, vice-president of marketing for Food Genius, a Chicago-based research firm. “This is a result of consumer demand and awareness of more healthy options when dining out, along with millennials’ and younger generations’ preference towards more flavorful ingredients.”

Salads are featured on more than half of restaurant menus, according to Food Genius, which tracked 63,483,789 items on 93,304 menus at 359,180 restaurant locations for its latest salad report.

Romaine is the most popular lettuce used in salads and four times more likely to be featured than iceberg lettuce or butterhead lettuce in restaurants. Other popular salad bases include spinach, arugula and cabbage.

The most popular protein is chicken, featured in 76% of salads on restaurant menus, followed by pork (45%), shrimp (33%) and tuna (25%). Tomato and onion top the list of toppings on salads in restaurants (67% and 57%, respectively), ahead of cucumber (44%), pepper (43%), olive (34%), crouton (34%) and red onion (28%). Croutons and bacon appear more frequently on casual-dining salads than on fast-food offerings, Food Genius said.

Dairy and cheese ingredients are featured on two-thirds of all salads in U.S. restaurants. Parmesan leads the pack, on 30% of salad entrees, followed by feta (25%), mozzarella (20%), blue cheese (16%) and cheddar (15%).

Most used dressings on salads are vinaigrette and Caesar. Balsamic vinaigrette is a fixture of fine-dining salads, while ranch is more common in quick-service restaurants. Lemon is the leading seasoning on salads (13%), followed by basil (12%), ginger (9%), cilantro (7%), lime (5%) and mint (5%).

Kale’s callout on menus has grown 45% between 2013 and 2014. Mesclun, butterhead lettuce arugula and red cabbage also are on the rise, according to Food Genius.

Among salad dressings, top-growing varieties include Russian, ranch, house, Italian and Caesar, while blue cheese and thousand island dressings declined slightly in usage. Overall, salad dressings have not changed significantly in usage, Food Genius reported.

National and regional chains are raising the bar on this menu mainstay with innovative new offerings. Saladworks, a fast-casual concept, recently introduced for a limited time a spring noodle salad, featuring fresh spring mix and a signature lettuce blend, sesame noodles, jumbo shrimp, carrots, edamame and snap peas with roasted peanuts and mandarin sesame ginger dressing.

A new seasonal offering from Gordon Biersch is the spinach, fruit and nut salad, featuring baby spinach tossed in lemon vinaigrette with dried cherries, minced pears, goat cheese, blueberries, raspberries, spiced pecans, sweet yellow peppers and a sprinkle of toasted almonds. The restaurant also is offering a beef tenderloin salad with baby spinach, warm bacon vinaigrette, avocado, tomatoes, gorgonzola cheese, roasted pancetta and crispy onions.

Wendy’s recently released a series of on-line videos to show customers how its salad ingredients are sourced and prepared. The chain offers three premium salads, including barbecue ranch chicken, apple pecan chicken, and Asian cashew chicken. Ingredients include roasted corn, edamame cranberries, and blue cheese crumbles. The company said fresh shipments of produce are delivered to each restaurant throughout the week and lettuce and other vegetables are chopped in the restaurants daily.

Noodles & Co. recently unveiled a line of Buff Bowls, which substitute spinach for the fast-casual chain’s typical pasta and double the vegetables. Varieties include Japanese Pan with marinated steak, Tuscan Fresca with grilled chicken breast, Bangkok Curry with organic tofu, and Pesto with pork.

The Pecanberry Salad returns to McAlister’s Deli through the summer. The seasonal item features strawberries, blueberries, candied pecans and grilled chicken on mixed greens with fat-free raspberry pecan vinaigrette dressing.

The California Fields Salad at California Pizza Kitchen includes fresh watermelon, strawberries and field greens with housemade champagne vinaigrette, feta and pistachios.

The new Tay’s Wedge Salad from Bonefish Grill contains tomatoes, Danish blue crumbles, chives, crispy onions and blue cheese dressing.

Among Seasons 52’s seasonal entree salads is the Maui Tuna Crunch, with sushi-grade seared tuna, organic greens, pineapple, toasted almonds and sesame dressing.

Uncle Maddio’s Pizza Joint recently introduced a new Thai-inspired salad, with red onion, sweet and spicy sriracha sauce, purple cabbage and grilled chicken.

A pair of salads on the spring menu at Corner Bakery Cafe feature fresh produce, nutritious grains and bold flavors. The Southwest Salad includes romaine lettuce, shredded cabbage, quinoa, black beans, English cucumbers, roasted corn and tomato salsa, and house-pickled jalapenos, topped with avocado citrus ranch dressing and crunchy tortilla strips. The Four-Grain Tabbouleh salad has a blend of quinoa, wheat berries, red rice and faro, plus diced tomatoes, English cucumbers and parsley in a light lemon dressing.