For the spinach and cheddar, sauté the spinach in a small skillet over medium heat for 1–2 minutes, just until wilted. Remove from heat and divide the spinach evenly among 6 muffin cups, then top with green onions and cheddar.
For the Mediterranean filling, mix the sun-dried tomatoes, feta, olives, and parsley in a small bowl. Divide evenly among 6 muffin cups.
For the mushroom, roasted red pepper, and Swiss, sauté the mushrooms and red peppers in a skillet over medium heat for 3–4 minutes, until softened and any moisture has cooked off. Remove from heat and divide evenly among 6 muffin cups, then top with Swiss cheese.
For the pesto Parmesan, add about 1 teaspoon Parmesan cheese to each of the remaining 6 muffin cups, followed by about 1 teaspoon pesto.
Spoon about 1 tablespoon of the egg mixture into each muffin cup, filling nearly to the top.
Bake for 20–22 minutes, until the eggs are set and the tops are lightly golden. The quiches will puff up while baking and settle as they cool.
Let cool for 5 minutes before removing from the pan.