In a large nonstick skillet, saute mushrooms and zucchini in 2 tablespoons butter until tender; remove and keep warm.
In the same skillet, melt remaining butter. In a small bowl, whisk the eggs, water, salt and pepper. Add to skillet (mixture should set immediately at edges). As eggs set, push cooked edges toward the center, letting uncooked portion flow underneath.
When the eggs are set, spoon vegetable mixture over one side and sprinkle with cheese. Fold other side over filling. Remove from the heat.
In a small saucepan over medium heat, melt butter. Add remaining sauce ingredients; cook and stir for 5 minutes or until heated through. Serve with omelet.