Prepare turkey patties. Combine ground turkey, parmesan, parsley, mayonnaise, garlic powder, and black pepper in a large bowl. Mix just until combined, being sure not to overmix. Shape the patties into 10 portions, rolling them into balls. Place on a baking sheet lined with wax paper and chill in the refridgerator for at least 15 minutes or overnight.
Prepare garlic buns. Combine softened butter with parmesan, garlic, parsley, and salt in a medium bowl. Spread butter on both sides of burger buns and place buns on a baking sheet with the buttered side facing up. Bake buns for 7-8 minutes or until toasted.
Pour marinara sauce in a medium saucepot and heat until warm. Set aside.
Preheat broiler to high.
Heat a large saute pan over medium-high heat. Remove the turkey patties from the refrigerator and lay patties in the pan, giving them plenty of space in between. You may need to cook the patties in batches. Smash the patties using a flat spatula until they're ¼-inch thick. Season generously with salt and cook utnil browned, about 2-3 minutes.
Flip patties over and cook for 2 more minutes. Remove from heat and spoon marinara sauce on each of the patties. Place a slice of mozzarella on top and broil for 2-3 minutes or until cheese has melted.
While the patties are broiling, toss together arugula with extra virgin olive oil and lemon juice. Season with salt and pepper and set aside.
Remove patties from the broiler and place on the toasted garlic buns. Top with arugula salad and remaining bun. Serve immediately.
Notes
The garlic butter for the buns and turkey patties can be prepared the day before. Cover the patties with plastic wrap if storing in the refrigerator overnight. Bring the butter to room temperature to soften before spreading on burger buns.