First, in a small saute pan, saute the mushrooms, peppers, and white onions over medium heat for four to five minutes. The vegetables should be fork tender.

Next, in a small bowl, whisk the eggs, similar to making scrambled eggs. After that, spray a large saute pan with non-stick cooking spray and pour the eggs into the pan. Let them cook over medium-low heat and do not mess with them.

After a few minutes, the eggs will cook all the way through. Don't worry about flipping them; they will cook thoroughly. If needed, poke a few small holes in the omelet where the eggs are still raw. 

Last, add the sauteed veggies and cheese to the omelette. Place them in the center of the dish, like you are making a burrito. Remove the pan from the heat. Use a spatula, and gently lift the edges of the mushroom omelette. Now, fold the eggs inward on all four sides of the veggies. You should have a cute egg burrito. Garnish it with the tomatoes and serve hot.