Chicken Burgers

Name: Chicken Burgers
Prep time: 10 min
Total time: 10 min
Cuisine: American
Ingredients: 1/2 c. mayonnaise; 3 tbsp. ketchup; 2 tbsp. finely chopped sweet gherkins, plus 1 Tbsp. juice from jar; 1 tbsp. yellow mustard; 1 tsp. Worcestershire sauce; 1/4 tsp. kosher salt; 1/4 tsp. smoked paprika; 1/8 tsp. freshly ground black pepper; 1/8 tsp. garlic powder; 3 tbsp. unsalted butter, divided; 1/2 medium yellow onion, finely chopped; Pinch of granulated sugar; Kosher salt; 2 lb. (93% lean) ground chicken; 3/4 c. panko; 2 tbsp. mayonnaise; 1 tbsp. Worcestershire sauce; 1 1/2 tsp. garlic powder; Freshly ground black pepper; 1 tbsp. extra-virgin olive oil; 6 slices cheddar cheese; 6 brioche burger buns, split, lightly toasted; Butterhead lettuce leaves, thinly sliced tomato, and thinly sliced red onion, for serving