Preheat the oven to 450°F (232°C).

Place cauliflower florets in the bowl of a food processor with the blade attached. Pulse until completely crumbled.

Pour the cauliflower into a microwave-safe medium-sized bowl and microwave on high for 5 minutes. Let it cool slightly.

Transfer cauliflower to a clean kitchen towel or cheesecloth and squeeze out all the excess liquid.

In a mixing bowl, combine the cauliflower with Parmesan, salt, and garlic powder. Stir until mixed well.

Add the slightly beaten egg to the cauliflower mixture and mix thoroughly.

Spray a 9-inch round tart pan or pie dish with nonstick spray. Pour in the cauliflower mixture and use your hands to mold it to the pan, pressing it firmly on the bottom and up the sides.

Bake the crust for 10 minutes. Then, lower the oven temperature to 400°F (204°C).

In a large mixing bowl, combine 5 eggs, milk (or heavy cream), 1 teaspoon salt, and black pepper. Whisk thoroughly and set aside.

In a small skillet, heat the olive oil over medium-high heat. Add the spinach and cook until just wilted, stirring often, about 2-3 minutes.

Remove the spinach from heat and add it to the egg mixture, along with the scallions and crumbled feta. Mix to combine.

Pour the egg and vegetable mixture into the cauliflower crust.

Bake for 15-20 minutes or until the quiche is set and slightly golden.

Let your Spinach and Feta Quiche cool slightly before serving. Optionally, you can top it with additional feta or Parmesan cheese.