What to do with those leftovers and close to becoming rotten vegetables...
6-8 eggs (for standard casserole size)
1/4 cup of milk (any type but not sweetened or flavored)
Leftover meats (optional)
Vegetables that you want to use before they rot (such as onion, tomato, spinach, cabbage, potato, broccoli, etc. This is entirely up to your likes and dislikes as well as what you have on hand)
Cooking oil of your choice
Preheat your oven to 350 degrees.
In a skillet with a little cooking oil, cook all vegetables over medium heat for 5-10 minutes (they don't have to be quite as soft as you would like yet, because they will cook more in your oven).
In a separate bowl, combine eggs, milk, salt, and pepper (like you are preparing to make scrambled eggs).
Grease your casserole dish.
In your greased casserole dish layer the skillet fried vegetables, along with any meats or cheese that you would like to incorporate (remember this is your creation based on what you have available, and that you like). You can lightly toss all the things in the casserole dish if you would like, just to mix it all up.
Pour your egg (milk, salt, etc.) mixture into the casserole dish on top of the vegetables/meats and give it a light jiggle.
Place it in your oven for 20 minutes. Check it at 20 minutes, it may not be done. Depending on the size you make and the ingredients that you have added it may take another 20 minutes to cook. Don't worry, it stays hot/warm for awhile so if it gets done quicker than you had planned it will be fine to wait a bit to eat it. You don't want to burn your tongue anyways.
If you want to make this into more of a quiche, you can make a hash brown crust by using either frozen shredded hash browns at the bottom of the casserole dish and baking those alone in the dish for 15 minutes prior to adding the things from the above recipe. You can also shred potatoes yourself (any kind of potato), mix the raw shredded potato with a small amount of cooking oil (lightly coat), lightly cover the bottom of your casserole dish with the mixture and then add the things from the above recipe (it may need to cook a little longer than 20 minutes, and you should see browning at the bottom when done).