Preheat your oven to 375°F.

Cook the spaghetti according to package instructions until al dente. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the minced garlic and red pepper flakes, sautéing for about 1 minute until fragrant.

Add the cooked spaghetti to the skillet, along with the marinara sauce, salt, and black pepper. Toss to combine and heat through for about 2-3 minutes.

Remove the skillet from heat and stir in the mozzarella cheese until melted and well combined.

While the pasta is heating, hollow out the sourdough bread bowls, leaving about a 1-inch border.

Fill each bread bowl with the cheesy spaghetti mixture, packing it in gently.

Sprinkle the tops with grated Parmesan cheese.

Place the filled bread bowls on a baking sheet and bake in the preheated oven for 15-20 minutes, or until the bread is crispy and the cheese is bubbly.

Remove from the oven and let cool for a few minutes. Garnish with fresh basil leaves if desired before serving.