Preheat oven to 375°. Coat 9 non-stick muffin cups (regular size) with cooking spray. Add cracker pieces in a mini food processor and pulse until crumbs form. Place 1 teaspoon of the crumbs evenly in the bottom of each muffin cup.
In a small bowl, combine thawed frozen spinach with red bell pepper. In another small bowl, combine shredded Gruyere with the green onions.
Spoon 1/2 tablespoon of the spinach mixture into each muffin cup. Then top that with a tablespoon of the cheese mixture. Add 1/2 tablespoon of the remaining spinach mixture on top of the cheese. Sprinkle ground nutmeg and freshly ground pepper over the top of each as desired.
In a small mixing bowl, beat milk and eggs together until well blended. Spoon 2 tablespoons (1/8 cup) of the mixture into each prepared muffin cup.
Bake until golden brown, about 20 minutes. Remove from oven and remove quiches from muffin cups with a fork or spoon and serve warm or at room temperature.