KANSAS CITY — Burgers for breakfast. Chocolate jalapeño milkshakes. Bunless sandwiches and crustless pizzas.

In the desperate fight for stomach share, fast-food chains are unveiling interesting menu innovation. Whether it’s a surprising flavor combination or trendy new ingredient, recent introductions reflect a marketplace wrought with heightened competition and continued macroeconomic pressure.

Fast-casual restaurants have snagged share from the quick-service segment, leading many chains to rethink their menu strategy. From over-the-top to better-for-you, recent launches and tests from top chains tap into consumer trends of health, customization, indulgence and adventure.

Burger King customers may soon order a Whopper with their morning coffee.

Burger King’s breakfast burgers

Burger King’s answer to the Waffle Taco? The Whopper.

As fast-food chains aim to improve their a.m. game, including Taco Bell’s big breakfast debut, Burger King is adding flame-broiled beef to the morning menu. Select lunch and dinner sandwiches and fries will be available during the day part alongside the chain’s regular breakfast selections of biscuit and croissant sandwiches.

The most important meal of the day has become a hot market for the food service industry. Restaurant breakfast day part sales were estimated to reach $47 billion in 2013, according to Rockville, Md.-based research firm Packaged Facts.

McDonald’s Shakin’ Flavor Fries

McDonald’s is testing customizable seasoned fries in select markets throughout Northern California and in St. Louis. Customers who order Shakin’ Flavor Fries pour a seasoning packet and the chain’s signature french fries into a bag and shake the contents to flavor the spuds. Seasonings include garlic Parmesan, spicy buffalo and zesty ranch. A similar item has been offered at McDonald’s restaurants in Hong Kong, China, India and Australia.

More chains recently have upgraded the sandwich’s sidekick. Fancier fries launched in recent months include sweet potato waffle fries from Jack in the Box, reduced-fat Satisfries from Burger King and Natural-Cut Fries at Sonic, which said the new skin-on french fries, made with whole russet potatoes, are crispier and fluffier than the chain’s original.

Sonic's chocolate jalapeno milkshake blends vanilla ice cream, chocolate sauce and bits of jalapeno.

Sonic Drive-In’s chocolate jalapeño shake

As part of its Summer of Shakes promotion, Sonic is offering more than two dozen milkshake varieties, including salted caramel, Oreo peanut butter, and chocolate jalapeño.

The latter contains vanilla ice cream blended with chocolate sauce and chunks of jalapeño, crowned with whipped topping and a cherry.

“After months of testing interesting but still delicious flavor combinations, we’ve created some seriously enticing shake flavors,” said Chef Claes Petersson, vice-president of product innovation at Sonic. “Salted caramel is a wonderful trend we were happy to embrace, and chocolate-covered jalapeño is a bold and fun twist on chocolate dipped fruit flavors.”

Domino's Specialty Chicken swaps pizza crust for hunks of breaded chicken.

Domino’s Specialty Chicken

A new platform from Domino’s Pizza dubbed Specialty Chicken features traditional pizza toppings, cheese and sauces layered on pieces of lightly breaded boneless chicken. Varieties include crispy bacon and tomato, spicy jalapeño and pineapple, classic hot buffalo, and sweet barbecue bacon. The launch represents Domino’s first since September 2012.

“Our pizza chefs have taken chicken to a whole new level, using our unique ingredients to create these four bold flavors,” said Russell Weiner, chief marketing officer for Domino’s. “There’s nothing quite like Domino’s Specialty Chicken on the market today.”

KFC: "Bread is dead."

KFC’s Double Down

For a limited time, the chicken chain has resurrected its famous bunless sandwich, which originally launched in 2010. A subject of comedian punchlines and cultish fanfare, the Double Down features bacon, Monterey jack cheese and sauce sandwiched between a pair of fried chicken filets. According to KFC: “Bread is dead.”

Hummus at Subway

Hummus has found a spot on the toppings table at Subway in select markets. The sandwich chain is testing the on-trend spread, adding a protein option for meatless sandwiches, according to the Associated Press.

The chickpea dip is associated with trends of health, Mediterranean flavors and premium ingredients. Panera Bread said it also is adding hummus to new sandwiches as a lighter alternative to oils and heavy dressings.

Baskin-Robbins is adding frozen Greek yogurt to its better-for-you selections.

Baskin-Robbins Greek frozen yogurt

Baskin-Robbins, a unit of Dunkin’ Brands, in May launched its first-ever frozen Greek yogurt option as part of its better-for-you menu. Super Yumberry Greek Frozen Yogurt, which is berry-flavored with a triple-berry ribbon swirl, has 130 calories and live active cultures per 2.5-oz scoop.