1. Cook the Spaghetti:

• Bring a large pot of salted water to a boil.
• Cook the spaghetti according to the package instructions until al dente.
• Drain the spaghetti and set it aside.

2. Sauté the Aromatics:

• Preheat your oven to 375°F (190°C).
• Spray a skillet with olive oil and heat over medium heat.
• Add the finely diced onion and sauté for 5 minutes until softened.
• Stir in the crushed garlic and cook for another minute.

3. Cook the Ground Beef:

• Add the ground beef to the skillet. Use a spoon to break it into smaller pieces while cooking.
• Cook until the beef is browned and fully cooked.

4. Add the Sauce Ingredients:

• Stir in the tomato paste, salsa, chicken or beef stock, and taco seasoning.
• Mix well and let the sauce simmer for 5–10 minutes, allowing it to thicken slightly.
• Toss in the diced red and green bell peppers and cook for an additional 2–3 minutes.

5. Combine Spaghetti and Sour Cream:

• Remove the skillet from heat.
• Add the cooked spaghetti and sour cream to the taco meat mixture.
• Toss everything together until fully combined. Season with salt and pepper to taste.

6. Assemble the Casserole:

• Grease a baking dish with olive oil spray.
• Spread the spaghetti mixture evenly into the baking dish.
• Sprinkle grated mozzarella and cheddar (or red Leicester) evenly over the top.

7. Bake the Casserole:

• Place the dish in the preheated oven.
• Bake for 20–25 minutes, or until the cheese is melted, golden, and bubbly.

8. Serve:

• Let the casserole cool for a few minutes.
• Garnish with fresh herbs like cilantro, or serve with sour cream or diced jalapeños for extra flavor.
• Serve hot and enjoy!