Preheat oven to 375 degrees. Pour marinara sauce into a large skillet or baking dish and set aside.
Heat olive oil in a skillet over medium heat. Add spinach and cook until wilted, then add garlic and cook for 30 seconds more. Remove spinach from heat and coarsely chop on a cutting board.
Place ground turkey in a medium bowl. Add chopped spinach, egg, breadcrumbs, crumbled feta cheese, oregano, salt, and pepper. Gently mix with your hands until ingredients are incorporated, being careful not to overmix to avoid toughening the meat.
Form about 2 tablespoons of the turkey mixture into a ball and place it in the skillet with marinara. Repeat with the remaining turkey mixture.
Bake turkey meatballs for 20-25 minutes, checking for doneness after 15 minutes, or until a thermometer inserted into the center of a meatball registers 165 degrees. Remove from heat. Garnish with parsley as desired and enjoy.
