1. Preheat oven to 350 degrees. Spritz a 9 inch baking dish with non-stick cooking spray.
2. In a large skillet, melt butter over medium-high heat. Add onion and mushrooms. Cook until tender, about 3 to 5 minutes.
3. Add ham and spinach to skillet and heat through. Stir in the cheese. Transfer to baking dish.
4. In a mixing bowl, whisk eggs. Pour eggs over ham and gently move ham and vegetables until the egg mixture is evenly distributed. Pat the quiche flat.