1. In a large skillet over medium heat, brown the ground beef until fully cooked. Drain excess fat.

2. Add the chopped onion and minced garlic to the skillet and sauté until the onion is translucent.

3. Transfer the beef mixture to a slow cooker. Add the crushed tomatoes, tomato sauce, tomato paste, red wine (if using), sugar, basil, oregano, parsley, crushed red pepper flakes, salt, and pepper.

4. Stir to combine all the ingredients. Cover and cook on low for 6-8 hours or on high for 3-4 hours.

5. About 20-30 minutes before serving, cook the spaghetti according to the package instructions until al dente.

6. Drain the spaghetti and add it to the slow cooker, mixing well to ensure the sauce coats the pasta evenly.

7. Allow the spaghetti to sit in the slow cooker for another 10 minutes to absorb the flavors, then serve hot.

For a vegetarian twist, substitute the ground beef with a mixture of diced vegetables such as bell peppers, zucchini, and mushrooms, or use a plant-based meat alternative. You can also add a splash of cream or a handful of grated Parmesan cheese towards the end of cooking for a richer sauce. If you prefer a spicier dish, increase the amount of crushed red pepper flakes or add a dash of hot sauce. For a gluten-free option, use gluten-free pasta instead of traditional spaghetti.