Grease a 9.5-inch ring or bundt pan. Line the bottom and sides with sliced cheese so there are no gaps.
In a medium bowl, mix spinach, ricotta, eggs, Parmesan, salt, pepper, and garlic powder until smooth.
Pour the mixture into the cheese-lined pan. Smooth the top and sprinkle extra Parmesan.
Cook covered on low-medium heat for 20 minutes in a snug pot or bake at 350°F for 25–30 minutes until set.
Let rest 5 minutes before flipping onto a plate. Slice and enjoy warm or chilled.
