Preheat oven to 350 degrees F; lightly spray a 12-cup muffin tin with nonstick spray and set aside.
Thaw frozen pie crusts, remove from tins and roll out on a floured surface; use a biscuit cutter to cut 1 1/2 – 2 inch circles from the crust dough.
Place crust dough in each muffin cup, pressing into the bottom and sides of each muffin cup.
Cook turkey bacon in a medium skillet over medium-high heat until crisp; drain and cool on a paper towel; crumble bacon when completely cooled.
In the same skillet, saute spinach and garlic clove until spinach is wilted, approximately 5 minutes; drain and set aside.
Using the same skillet, saute onion until it begins to soften, approximately 3-5 minutes; drain and set aside.
Mix eggs, milk, cheese, bacon and salt until well combined; stir into spinach and add onions; mix well.
Spoon egg and spinach mixture into each muffin cup, filling about 2/3 full.
Bake for 20-25 minutes, or until quiches are puffy and golden brown.
Remove and cool on a wire rack before serving.