Slice sweet potatoes into thin rounds about ⅛-inch thick. Arrange them in a greased 9-inch pie dish, overlapping slightly to cover the bottom and sides. Brush with olive oil and season with salt and pepper.
Bake the sweet potato crust at 400°F (200°C) for 20 minutes until softened and lightly golden. Allowing the crust to bake first helps it hold the egg filling without becoming soggy.
Heat olive oil in a skillet over medium heat. Add spinach and cook for 2–3 minutes until wilted. Remove excess moisture before adding it to the filling.
Whisk eggs in a bowl until combined. Add cooked spinach, feta cheese, garlic powder, black pepper, and salt. Stir gently until evenly mixed.
Pour the spinach and feta egg mixture into the baked sweet potato crust. Spread the filling evenly without overfilling the dish
Bake at 375°F (190°C) for 30–35 minutes until the center is set. The middle should have a slight wobble but should not appear liquid.
Let the quiche rest for 10–15 minutes before slicing. Serve warm with salad, roasted vegetables, or fresh fruit.
