Preheat your oven to 375°F (190°C) and lightly spray a muffin pan with cooking spray to prevent sticking.

Slice the mushrooms into ¼-inch thick pieces and roughly chop the fresh spinach, keeping them separate.

Heat 1 tablespoon of oil in a skillet over medium-high heat. Add the sliced mushrooms and sauté for 2-3 minutes until they start to soften. Then add the chopped spinach and cook for an additional 1 minute until wilted. Remove from heat and let cool slightly.

In a large mixing bowl, whisk together the 4 large eggs until well combined. Add in the finely grated parmesan cheese, 2 tablespoons of milk, garlic powder, optional onion powder, salt, and black pepper. Mix everything together until smooth.

Gently fold the cooled sautéed mushrooms and spinach into the egg mixture until evenly distributed.

Pour the combined mixture into each muffin cup, filling them about three-quarters full to allow space for rising.

Place the muffin pan in the preheated oven and bake for 18-20 minutes, or until the muffins are set with a slightly jiggly center.

Remove the muffin pan from the oven and allow the quiche muffins to cool in the pan for 5 minutes. Then transfer the muffins to a wire rack to cool completely.