Measurements are approximate - this is something I made up as I went and I didn't do it with recipe development in mind. Still it's an easy recipe of sorts- just try it and don't fret over the approximate measurements.
Crack 9 eggs in a bowl and beat well. Add salt and pepper, stir well. Set aside. Sautée onion in oil till translucent. Set aside.
Preheat oven to 375°. In the meantime lightly grease your muffin pan with either a spray or a little oil on a paper towel.
Into the greased muffin cups, add about 3 or 4 leaves of spinach. Top the spinach with about a teaspoon of sautéed onions. Top the onions with about 1 tablespoon of shredded cheese. Then using a soup ladle, add enough egg mixture to fill the muffin tin, about 2/3 full.
Bake your little breakfast quiches for about 10 to 20 minutes, depending on the size of your muffin tin cups. They should brown nicely on the top, but be careful not to overcook. To test for doneness, insert a toothpick in the middle of one of the muffin cups. If the toothpick comes out clean, then your quiches are done! Let them cool for at least 10 minutes in the pan. Using a dinner knife, carefully run the blade around the perimeter of each little quiche and plop them carefully onto a plate to finish cooling. Makes a dozen.