I'm a big fan of frittatas because they are so easy to make and you can cook everything in one pan, making clean up so much easier. And they are so easily adapted based on ingredients you have on hand. Switch out the mushrooms with red bell peppers or asparagus. Use kale or Swiss chard in place of spinach.
And if you want to make an even tastier meal, serve it with a salad like this Fennel and Orange Salad.