Preheat the Oven: Begin by preheating your oven to 375°F (190°C).
Prepare the Bread Dough: On a lightly floured surface, roll out the bread dough into a rectangle about 0.5 inches thick. Ensure it's pliable to allow for easy handling.
Make the Filling: In a large mixing bowl, combine the chopped spinach, sharp cheddar cheese, mild cheddar cheese, melted butter, garlic, onion powder, Italian herbs, salt, pepper, and crushed red pepper flakes (if using). Mix until ingredients are well incorporated.
Cut the Dough: Using a sharp knife, cut the dough into squares (about 2x2 inches) or strips. This will allow you to easily pull them apart later.
Fill the Dough: Spoon a generous amount of the cheese and spinach mixture onto each piece of dough. Make sure to distribute the filling evenly, so every pull-apart piece is loaded with cheesy goodness.
Stack the Dough: Layer the filled pieces on top of each other, then stand them upright in a greased loaf pan. This will give your pull-apart bread its iconic shape.
Let it Rise: Cover the loaf pan with a clean kitchen towel and let it rise in a warm place for about 30 minutes, or until it has doubled in size.
Bake the Bread: Once risen, place the loaf pan in the preheated oven. Bake for 25-30 minutes, or until the top is golden brown and the cheese is bubbly.
Cool and Serve: Remove the bread from the oven and allow it to cool for about 10 minutes. Garnish with fresh parsley before serving.
Pull Apart & Enjoy: Serve warm and enjoy pulling apart the layers filled with cheesy, spinach deliciousness!