SUPER BASIC RECIPE/TIPS
The basic method I follow is cook up whatever veggies/meat/deliciousness I want in my quiche until it is cooked well enough to just eat on its own, toss it with whatever cheese I want and about half fill a frozen pastry crust with it. I beat together eggs, milk, salt, pepper (sometimes other stuff like onion/garlic salt or oregano) and sometimes additional cheese and pour it over the "stuffs" to just about fill up the rest of the crust (keep in mind the eggs expand), and cook in a 350F oven until the center is set (about 35-45 minutes).
Have fun mixing and matching your fillings. Below I typed up the quiche I made this weekend with the most "stuffs", but the other one just had steamed broccoli with a bit o' garlic and a ton of cheddar cheese.
ACTUAL DETAILED RECIPE
Frozen pastry crust, deep dish means more STUFFS! (optional if you don't like crusts)
Onion, maybe a half or less depending on how much you want, cut into long thin strips
Garlic, 2-3 cloves minced
Mushrooms, about a cup, chopped into about 1/2" pieces
Sausage, 3-4 links or patties, fully cooked and chopped up
Eggs, 3-4 depending on how much stuff/how deep your crust is
Milk, about a half cup
Baby spinach, handful of leaves, chopped or torn into slightly smaller pieces
Preheat oven to 350F.
Cook the onions in the butter over low heat for a while until they start getting really soft (you want them to end up caramelized or near enough by the time your whole veggie mixture is done). Add the garlic and cook a bit longer. Toss the mushrooms in and cook a bit more. Everything should be getting slightly golden/brown and soft. Toss the baby spinach in and cook just long enough to wilt it/coat it with butter. Note: I usually end up constantly adding butter in small bits to make sure it gets on everything. You don't want the food to burn but you don't want it to be swimming in butter either.When it looks good and cooked, remove from heat.
Toss your cooked veggie mixture with the chopped up sausage and feta and put it on the bottom of your pastry shell, or if you are going the crustless route, on the bottom of a greased pie dish. You want the filling stuff to about half fill your dish, if you have more than that it might not hold together with the egg, if you have too little it won't be overbrimming with delicious stuffs.
Beat your eggs and milk together with salt/pepper/any additional seasonings you want (I put in a little oregano on Saturday). Pour over the stuffs until your crust/dish is just about full. Sprinkle some cheddar over the top.
Pop the whole shebang in the middle of your oven and cook until the center is set (when you wiggle it, the center doesn't look liquidy). About 35-45 minutes.