Preheat the oven to 450 degrees. Thaw the frozen spinach in the microwave or at room temperature until it is no longer in large clumps. Add the garlic powder, salt, and crushed red pepper flakes. Stir to distribute the spices. Add the mozzarella and stir to combine again.
Prepare a pizza pan with non-stick spray or cornmeal. Stretch the dough out into a 12" circle and place on the pizza pan. Brush 1 tablespoon of olive oil over the surface. Spread the spinach and cheese mixture over the dough. Thinly slice the red onions and sprinkle over top. Crumble the goat cheese over the pizza.
Bake the pizza for 10 minutes or until the crust and goat cheese crumbles are lightly browned. Slice into 6 pieces and serve.