Preheat grill to medium (375º-425º). Scoop 1 avocado into a medium bowl and mash with a fork. Add turkey, garlic, salt and pepper to bowl. Gently mix until evenly incorporated, being careful not to over mix.

Divide and shape into four equal-size patties. Using your thumb, create a dent in the center of the patty, which allows for more even cooking. Place on grill and cook 6 minutes per side flipping once, or until the internal temperature reaches 165º. Remove from grill, tent with aluminum foil and let rest for 5-10 minutes.

Slice the second avocado and top each burger with 3 slices.