This is taken from a Bittman article in the NYT which promotes frittatas with a higher ratio of vegetables to egg than is customary. The recipe is exemplifies just one combination of vegetables - many others are possible. He also suggests adding parmesan for a touch of “luxury”.
Put olive oil in a skillet (preferably nonstick or well-seasoned cast iron) and turn heat to medium.When fat is hot, add onion, if using, and cook, sprinkling with salt and pepper, until it is soft, 3 to 5 minutes.
Add vegetables, raise heat and cook, stirring occasionally until they soften, from a couple of minutes for greens to 15 minutes for sliced potatoes.
Adjust heat so vegetables brown a little without scorching. (With precooked vegetables, just add them to onions and stir before proceeding.)
When vegetables are nearly done, turn heat to low and add herb. Cook, stirring occasionally, until vegetables are tender.
Pour over vegetables, distributing them evenly.
Meanwhile, beat eggs with some salt and pepper, along with cheese if you are using it.
Cook, undisturbed, until eggs are barely set, 10 minutes or so; run pan under grill for a minute or 2 if top does not set.
Cut frittata into wedges and serve hot, warm or at room temperature.