In a medium bowl, beat egg white until fluffy. Stir in parsley, garlic, onion, peppers until fully mixed.
Place turkey in the bowl and mix up with hands until everything is fully incorporated.
Add panko and mix gradually until well distributed.
Place a large pan over medium heat with a drizzle of olive oil.
Divide turkey mixture in half and place each half on its own piece of wax paper and shape into a large, flat patty.
When the pan is hot, place each patty and cook 10 minutes on each side or until the center of the largest part reaches at least 165°.
When patties are cooked, place cheese on top and cover for 3 minutes, or until cheese is melted to your liking.
Transfer patties to your toasted buns; garnish with mayo, mustard, tomato, and sliced onion. Go to town!