Add the browned ground beef, chopped onions, taco seasoning, and can of Rotel to a large resealable freezer bag. Seal and remove excess air.
Freeze.
Thaw.
When you’re ready to start cooking, place the contents of the large bag, water, and uncooked spaghetti noodles into a very large flat-bottomed skillet. Cook over high heat until the mixture comes to a boil.
When the pasta is cooked through, remove the lid and sprinkle with cheese. Stir to melt the cheese into the pasta and serve immediately.