Preheat your air fryer to 360°F and lightly grease it with non-stick spray. In a large mixing bowl, gently combine the ground chicken, onion, spinach, dijon mustard, minced garlic, parsley, paprika, salt, and pepper. You can add red chili flakes for spice if desired. Do not over-mix, or the burgers will be tough.
Divide mixture and make 4 burger patties, about 1/2-inch thick.
Gently place each burger into the preheated air fryer basket, making sure they are evenly spaced out. Do not let the burgers overlap. If your air fryer is small, do two batches.
Air fry for a total of 10 - 13 minutes, flipping the burgers halfway through. The internal temperature of each burger should be 165°F. Over-cooked chicken burgers will be dry.
If you are adding cheese, place one slice of cheese on top of the chicken patty in the last 1 minute of air frying.
If serving with buns, you can toast them in the air fryer after the burgers are done, in a toaster oven, or on the stovetop. Lightly butter them and air fry at 300°F, cut side up for 3 - 4 minutes until golden. You can also serve these burgers in lettuce buns or on a salad if you want to make it low-carb.
I top mine with thinly sliced red onion, lettuce leaves, sliced tomato, and cheddar cheese. Enjoy!