This spinach and mushroom frittata is an easy, protein-packed meal that feels a little fancy with almost no effort. Sautéed onion, crimini mushrooms, and spinach get folded into fluffy eggs and tangy goat cheese, then finished in the oven until perfectly set. Top with a few halved grape tomatoes for a fresh pop of flavor, and broil briefly for a lightly golden top. Perfect for breakfast, brunch, or a quick weeknight dinner.