Cook pasta until al dente. It varies depending on the brand that you will use. Drain and set aside.
Saute onions and tomatoes until cooked. Mix in tuna with some of the remaining liquid (do not drain all) from the can and bell pepper. Add salt and pepper to taste. Add oregano but before adding smash it first in your palm to release the aroma of it. Simmer for 5 minutes.
Pour the mixture on top of the cooked noodles and add the cheez whiz while the mixture is hot. Add salt, pepper and oregano to taste.