Cook bacon in a nonstick skillet until crisp; remove bacon, and crumble. Reserve 2 tablespoons drippings in skillet.
Sauté mushrooms in reserved drippings until tender. Add fresh spinach, and cook 3 minutes. Remove mixture from skillet.
Whisk together eggs and next 3 ingredients until frothy; stir in hash browns and 1 1/2 cups cheese. Pour into skillet, and cook over medium heat. As egg mixture starts to cook, gently lift the edges of omelet with a spatula, and tilt pan so uncooked portion flows underneath. Top with spinach mixture and tomato; cover and cook 3 more minutes or until omelet is set. Fold over in half; place on a serving plate. Sprinkle with remaining 1/2 cup cheese and bacon.