In a large skillet over medium heat, add ground beef or turkey. Cook for about 5-7 minutes, breaking it apart with a spoon until it's browned and cooked through.

Stir in the taco seasoning and diced tomatoes, mixing well to combine. Cook for an additional 2 minutes.

Add uncooked spaghetti to the skillet, ensuring it's evenly spread out. Pour in about 4 cups of water to cover the pasta. Bring to a boil, then reduce heat to low and simmer for about 10-12 minutes.

Once the spaghetti is cooked, remove from heat and stir in the shredded cheddar cheese gradually.

Scoop the cheesy taco spaghetti onto plates or into bowls, optionally garnishing with sour cream, chopped avocado, or fresh cilantro.