In a small bowl, whisk eggs, 1 tablespoon water, salt and pepper until blended.
In a medium nonstick skillet, heat oil over medium heat.
Add onions and cook until tender and golden, 3 to 4 minutes.
Add the mushrooms and cook and stir for 3-4 minutes or until tender.
Add spinach; cook and stir until wilted.
Add egg mixture; cook and stir just until eggs are thickened and no liquid egg remains.
If you want to add cheese, add it with the eggs.