Heat oil in a nonstick pan on medium heat. Add, diced onion, asparagus, and sliced mushrooms. Saute for 3 minutes over medium heat.
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 cheese. Slip the spatula under the omelet and fold over. (If making multiple omelets store the cooked ones on a baking sheet in the oven until all are finished)
Heat a nonstick pan on medium heat and brown the chicken sausage on both sides. Serve on the side of the omelet with toast and plums.