Melt butter in a saucepan over medium heat, then add onions and bell peppers.
Cook onion and pepper until soft, but not browned.
Stir in the diced ham and cook until the ham is limp and heated through. Remove immediately from heat and set aside.
Add eggs, water, and salt to a mixing bowl. Combine them well and beat them well. Place the bowl aside.
Add a little oil to a 12-inch frying pan and heat on medium-low. It's best to use a nonstick pan.
Sprinkle the egg mixture with onions, bell peppers, ham, tomato if you wish, sausage, bacon, and half the roast beef, along with 1/2 cup of shredded cheese, in the pan.
Cover the omelette until it begins to set. Fold the omelette from the sides to the centre as soon as you remove the lid. Fold in half if it is difficult.
Add the remaining cheese and roast beef. Serve with a side of Picante Sauce or Sour Cream and diced green onions.