Frittatas are one of our favorite prep-ahead breakfasts because they're simple to make and reheat quite well (we even enjoy them straight out of the fridge or at room temperature). The key to a fluffy frittata is to add a splash of water and whisk your eggs until well combined. We fill this frittata with tender zucchini, fresh sun-dried tomatoes and feta cheese for the ultimate way to start your day!