In a bowl, mix together eggs, salt, and pepper until well blended.
Chop mushrooms then stir into eggs.
Heat a large nonstick skillet over medium-high heat; reduce heat to medium and spread spinach over the bottom.
Pour egg mixture over spinach and cook about 1 minute, lifting edges occasionally to allow uncooked egg mixture to flow to bottom of the skillet.
When mixture begins to set around the edges, reduce the heat to medium-low, cover, and cook 3-6 minutes more until completely set.
Sprinkle cheddar cheese over half of the eggs, then fold the other half over top.
Cut the omelet into quarters and slide each piece onto a serving plate.
Top with Parmesan cheese and serve with grapes on the side.