To prepare sauce, combine first 6 ingredients, stirring with a whisk until smooth.
To prepare burgers, place onions and next 5 ingredients (onions through chicken) in a food processor; process until coarsely ground. Divide mixture into 4 equal portions, shaping each into a 1/2-inch-thick patty.
Place patties on a grill rack coated with cooking spray; grill 4 minutes on each side or until done. Place rolls, cut sides down, on grill rack; grill 1 minute or until toasted. Place 1 patty on bottom half of each roll; top each serving with 1/4 cup sprouts, about 1 tablespoon sauce, and top half of roll. Yield 4 servings.