1. With clean hands, combine chicken, zucchini, bread crumbs, Parmesan, Italian seasoning, garlic powder, salt and pepper in a large bowl. Form into 4 patties.
2. Heat oil in a large nonstick skillet over medium heat. Add patties and cook until browned on one side, 4 to 6 minutes. Carefully flip. Pour equal amounts marinara over each patty, then top with 1 slice provolone apiece. Cover and continue cooking until patties are cooked through, 4 to 6 minutes more. Top with spinach and serve on buns.