Baking Sheet: Put a large piece of parchment paper on a baking sheet. Set aside.
Grate: Place a cheese grater on top of 2-3 pieces of paper towel. Grate the white onion on top of the paper towel. Use the paper towel to gently squeeze out as much of the excess moisture from the onion. Use the same cheese grater to shred the frozen butter (if using).
Burger Patties: Put the shredded onion and frozen butter in a large bowl and add 1 pound ground chicken, ¼ cup almond flour, 2 tablespoons parmesan cheese, 2 tablespoons mayonnaise, 2 teaspoons garlic, 1 teaspoon worcestershire sauce, 1 teaspoon dijon mustard, and ½ teaspoon lemon zest. Mix to fully combine.
Chill: Divide meat mixture into 4 equal patties about ½ - ¾ inches thick. Place them on a parchment lined baking sheet and create an indent in the middle of each patty. Place baking sheet in the freezer for 20 minutes to help patties keep their shape.
Prep: Ensure grill grates are clean and heat grill to medium-high heat.
Grill: Remove patties from freezer and season the top generously with kosher salt and ground black pepper. Take a piece of paper towel and put a little olive oil on it - hold it with a pair of tongs and rub the olive oil on the hot grill carefully. Place burgers on the grill over direct heat and close the lid. Let cook 5-6 minutes per side or until they reach 160℉ internal temperature.
Add Cheese: Place fresh mozzarella slices on top of burgers during the last 2-3 minutes of cook time. Move burgers to indirect heat if you need a bit more time. Remove and let rest 5 minutes.
Build burger: Place fresh basil on top of the bottom bun. Follow with chicken burger, tomato, balsamic glaze and top bun. Enjoy!
Notes
*Frozen Butter - if you are looking to really keep these chicken burgers lean, you can definitely omit the butter BUT if you are just looking for a juicy chicken burger then definitely include this step!
Make ahead: feel free to make the patties the day before. Store in an airtight container in the refrigerator.
Freeze: to make these ahead and freeze simply make patties and then place a piece of parchment between them as you stack. Place in a freezer-safe bag, label and place in freezer for up to 3 months. Let thaw overnight and then grill according to the instructions above.