In a large skillet or sauté pan, heat the olive oil over medium heat.

Add the diced red onion and ground beef. Use a spatula to break the beef into small pieces as it browns for about 6–8 minutes, until the onions are softened. Drain excess grease if necessary.

Sprinkle in the taco seasoning, then add the undrained Rotel, dry spaghetti, and water directly into the skillet.

Stir everything well to combine and bring the mixture to a boil over medium-high heat.

Reduce the heat to low, cover, and let it simmer for 12–15 minutes, stirring occasionally until the pasta is tender and most of the liquid has absorbed.

Once cooked, remove from heat and stir in the shredded cheddar cheese until melted and fully integrated.

Dish out the cheesy taco spaghetti hot and enjoy! Garnish with chopped fresh cilantro or extra tomatoes if you’d like.