In a large bowl, mix together the ground chicken, onion, breadcrumbs, egg, garlic, salt, and pepper. Shape the chicken mixture into 4 even patties. Using your thumb, press a divot into the center of each patty to help prevent it from puffing up during cooking.
Preheat a grill or large skillet over medium-high heat. Brush the grill grates with the oil or add the oil to the skillet and tilt the skillet to evenly coat the bottom. Cook the chicken patties, in batches if needed, until browned and cooked through (reaching an internal temperature of 160°F), 3 to 4 minutes on each side. If topping burgers with cheese, place 1 slice of cheese on each patty during the last minute of cooking.
Serve patties on hamburger buns with desired toppings.
Notes
Beat the egg before you add it to the chicken. That way, when you add it to the chicken, you can just incorporate the ingredients instead of also making sure the egg is whipped. Over-mixing the burger ingredients will yield a tough chicken patty.
Don’t over-mix! Over-mixing is often the culprit when it comes to a tough chicken burger. To keep them tender, gently mix together the ingredients without smashing or pressing the mixture together too much. Stop once everything is just incorporated.
To prevent the burger patties from puffing up while they cook, simply press a divot into the center of each patty with your thumb or a teaspoon.
Topping ideas: Sliced or smashed avocado, crispy bacon, lettuce, tomato, cheese, thinly sliced red onion, ketchup, mustard (Dijon mustard is a favorite in my house!), or mayonnaise are all excellent options for delicious chicken burgers! Mix it up with various types of cheeses like sharp cheddar, swiss, crumbled blue cheese, or a slathering of pimento cheese. Or, add a spicy kick with a sweet-and-spicy jalapeño jelly!