Turkey Meatballs

Name: Turkey Meatballs
Ingredients: 2 tablespoons olive oil; 1 onion, finely chopped; 1 rib celery, finely chopped; 1/2 small red bell pepper, seeded and finely chopped; 2 cloves garlic, finely chopped; 1 pound ground turkey; 1/2 cup quick-cooking (not instant) oats; 1/2 cup grated Parmesan, plus more for serving; 1 teaspoon Worcestershire sauce; One 10-ounce package frozen chopped spinach, thawed and excess moisture squeezed-out; Kosher salt and freshly ground black pepper; 4 cups prepared marinara sauce; Warm cooked spaghetti, for serving