Brown ground beef with salt, pepper and onion to taste in a large stockpot or Dutch oven medium high heat. Drain excess fat and stir in taco seasoning.
Stir in Ro*Tel, tomato paste, spaghetti and 3 cups water. Bring to a boil. Cover, reduce heat and simmer until pasta is cooked through, about 13-16 minutes.
Remove from heat and top with cheeses.
Cover until melted, about 2 minutes. Serve immediately, garnished with tomato and cilantro, if desired.