Step 1: Prepare the Ricotta Filling

In a medium bowl, combine the ricotta, shredded mozzarella, Parmesan, garlic powder, oregano, salt, and pepper. Stir well until all the cheeses are mixed evenly. Set aside.

Step 2: Sauté the Spinach

Heat 1 tablespoon of olive oil in a small pan over medium heat. Add the chopped spinach and cook for 1-2 minutes, just until wilted. Remove from heat and let it cool slightly. Once cooled, fold it into the ricotta mixture.

Step 3: Assemble the Sandwich

Take two slices of sourdough bread and spread the ricotta mixture evenly on one side of each slice. Sprinkle the chopped sun-dried tomatoes over the ricotta layer. Place another slice of bread on top to form a sandwich.

Step 4: Grill the Sandwich

Heat a skillet or griddle over medium-low heat. Spread butter on the outer sides of both slices of bread. Place the sandwich in the skillet and cook for 3-4 minutes per side, pressing lightly with a spatula, until golden brown and crispy.

Step 5: Serve and Enjoy

Remove the grilled cheese from the pan, let it rest for 1 minute, then slice in half. Serve hot and enjoy with a side salad, soup, or dipping sauce!