Preheat your oven to 375°F (190°C). Peel the sweet potatoes and slice them into thin rounds, about 1/8-inch thick.

Lightly grease a 9-inch pie plate with olive oil cooking spray. Arrange sweet potato slices in a spiral pattern to cover the bottom and sides.

Bake the sweet potato crust in the oven for 15 minutes.

In a skillet over medium heat, drizzle extra-virgin olive oil and sauté diced onion until translucent. Add minced garlic and spinach; sauté for 2 more minutes.

Whisk together eggs and Greek yogurt in a mixing bowl. Stir in feta cheese, salt, pepper, and optional crushed red pepper.

Spoon the sautéed vegetable mixture into the pre-baked crust, pour the egg mixture over it, and top with sliced Roma tomatoes.

Bake the quiche for 30 to 35 minutes until the egg is set and golden.

Let it cool for 5 to 10 minutes before slicing and serving.