Preheat oven to 200 degrees. (If making multiple omelets store the cooked ones on a baking sheet in the oven until all are finished)
Heat oil in a nonstick pan on medium heat. Add, diced onion and spinach. Saute for 2 - 3 minutes until its wilted.
In a bowl whisk the eggs with a pinch of salt and pepper. Toast the bread
Pour the eggs into the pan. As the eggs set around the edge of the pan, with a spatula, gently lift the egg to allow uncooked egg to flow underneath. When eggs are almost set on the surface but still look moist, add the tomatoes and cheese. Slip the spatula under the omelet and fold over.
Serve with corned beef hash (see recipe) and grapes on the side.