A frittata is the savvy cook's solution for leftovers, including vegetables, Easter ham, Passover brisket, roasted chicken, salmon, or pasta. It's also a perfect party appetizer, since it's equally delicious served warm, at room temperature, or cold.
Preheat the oven to 325 degrees. In a large bowl, beat eggs and stir in vegetables and/or meat, cheese, herbs, and salt and pepper, if needed.
Heat a 10-inch ovenproof skillet over medium heat for 2 minutes. Add oil and carefully swirl around to completely coat the bottom and sides of the skillet.
Add egg mixture, spread out evenly and cook, without stirring, until the edges and bottom are set and golden brown, 8 to 10 minutes. (Carefully loosen an edge to peek.) Transfer the skillet to the oven and bake until eggs are completely set and frittata is deep golden brown on the bottom, about 15 minutes more.
Remove the skillet from the oven. (The handle will be hot!) Loosen edges and bottom of frittata with a table knife and spatula; carefully invert onto a large plate. Serve warm, at room temperature or cold, cut into wedges.