Place ground beef and half the diced onion into the pan. Cook until ground beef is browned.
Add in taco seasoning and stir well. Pour in rotel and tomato sauce. Let cook on medium heat for 3 to 5 minutes.
Add in diced tomato and onion. Remove from heat.
Top with cilantro and cheddar cheese.
For Instant Pot:
Set instant pot to saute mode. Place in ground beef and half the onion. Saute until meat is browned. Add in taco seasoning and stir well.
Break pasta in half and place over the meat. Top with tomato sauce and rotel. Pour in 1 and 1/2 cups water.
Turn off saute mode and place lid on instant pot. Set to high pressure for 10 minutes. Once it stops counting release pressure and open lid.
Move pasta around to make sure non is sticking together. Place lid back on pot and set to high pressure for an additional 5 minutes. Release pressure when it's done counting. (If using thin spaghetti cut pressure times in half).
Once the pasta is done you can top with with the remaining onion and tomato. Toss well.