Preparing the Patty Mixture
Finely chop or pulse 2 boneless, skinless chicken breasts in a food processor until ground, or dice very small by hand. Transfer to a bowl and add 10 ounces cooked bacon (crumbled), 2 tablespoons finely minced fresh rosemary, ¼ cup grated or very finely minced yellow onion, 1 large egg, ½ cup plain breadcrumbs (or panko), 1 teaspoon kosher salt, and ½ teaspoon black pepper. Mix gently until everything is just combined, being careful not to overwork the mixture.
Forming the Patties
Divide the mixture into 4 equal portions and shape into burger patties, pressing them firmly so they hold together. Place the patties on a plate and refrigerate for about 15–20 minutes to help them firm up before cooking.
Cooking the Patties
Heat a skillet or grill pan over medium heat with a light drizzle of oil if needed. Cook the patties for about 5–6 minutes per side, until nicely browned on the outside and fully cooked through in the center. If adding cheese, place a slice of fresh mozzarella or provolone on each patty during the last minute of cooking and cover briefly to melt.
Making the Lemon-Garlic Aioli
In a small bowl, whisk together ½ cup mayonnaise, 1 tablespoon fresh lemon juice, 1 teaspoon lemon zest, 1 clove finely minced or grated garlic, ¼ teaspoon kosher salt, and ⅛ teaspoon black pepper until smooth and well combined. Chill until ready to use.
Preparing the Buns
Slice 4 burger buns (brioche or sturdy rolls) and lightly brush the cut sides with olive oil. Toast them in a skillet or on a grill until lightly golden and crisp.
Assembling and Serving
Spread a generous layer of the lemon-garlic aioli on the toasted buns. Add the cooked patties, then layer with tomato slices and baby arugula or spinach. Close the burgers and serve immediately while warm.
