This recipe is a healthy and flavorful twist on traditional tacos. Roast the spaghetti squash in the oven and set aside. In a pan, cook ground beef or turkey until browned, then add diced onions, garlic, and taco seasoning. Add canned black beans and corn, and cook until heated through. Add the cooked spaghetti squash to the pan and stir until everything is combined. Serve the mixture in taco shells or lettuce cups, and top with shredded cheese, diced tomatoes, and avocado.