I suppose a frittata could be described as baked scrambled eggs.  However, technically, it is an unfolded omelet native to Italy.  The ingredients are incorporated into the eggs, which are initially cooked in a fry pan on top of the stove.  After it begins to set, it is usually moved to the oven to finish cooking.  There are two other alternative ways to finish the cooking:  the whole frittata is flipped in the pan, or moved under the broiler.

An advantage of a frittata over an omelet, is that you can cook a lot of eggs at once, enough to serve all of your family or guests.  You can all sit down together to eat and converse.

A quiche, French in origin, is similar to a frittata.  I believe the difference is that a quiche is not started on top of the stove and is usually baked in a pie crust.

The technique and recipe I describe below is not a true frittata.  It is not started on the stove top.  It is half way between a frittata and a quiche.

Do not be intimidated by all the ingredients.  It is really easy to make.

3/4 cup chopped green pepper
1 1/2 cups sliced mushrooms
1 1/2 cups chopped zucchini
3/4 cup chopped onion
1 large garlic clove, minced
3 tablespoons of extra virgin olive oil
6 large eggs beaten
1/4 cup light cream
1 pound cream cheese, cut into small cubes
1 1/2 cups shredded cheddar cheese
2 cups cubed good white bread
1/4 to 1/2 teaspoon sea salt, or four or five grinds
1/4 to 1/8 teaspoon pepper, or a few grinds

Heat a fry pan to medium and add oil.  Let oil heat for a minute.  Sauté pepper, mushrooms, zucchini, onion, and garlic until zucchini is crisp-tender.  Cool slightly.  Beat the eggs with cream; then add cream cheese, cheddar cheese, bread, salt, pepper, and sautéed vegetables.  Fold well.

Pour into a greased (with butter) 10" spring form pan, or porcelain pie or quiche dish.

Bake in preheated 350° oven for 1 hour or until set in center.  It will probably be done in 35 minutes in an 11" or 12" quiche dish, because it is shallower.  Check by inserting a table knife to see if it comes out clean.  Cool 10 to 20 minutes before cutting into wedges to serve.  The frittata keeps its heat, so warn company to start with a little bite.

Variations:
Use fresh asparagus as one of the vegetables.  
Use yellow squash instead of zucchini.
For color, use some sweet red, orange, or yellow pepper in place of some of the green pepper.
Add some cooked bacon, ham, or sausage.