Preheat oven to 375F. Divide pizza dough into 4 equal pieces. Roll each into a ball, then press and stretch into a 6-inch circle. Press each circle into an oven-safe bowl, letting excess drape over the rim. The dough should be about 1/4 inch thick on the bottom and sides.

Mix melted butter, minced garlic, and Italian seasoning in a small bowl. Brush this mixture generously all over the dough, inside and out, including the draped edges. Sprinkle 1 tablespoon Parmesan inside each bowl.

Place bowls on a baking sheet and bake for 18-22 minutes, until the bread is deep golden and crisp. The overhanging edges should look like a frilly crust. Remove from oven and let cool 5 minutes. Carefully lift bread bowls out of their molds (they should release easily) and return to the baking sheet, hollow-side up.

While bowls bake, bring a large pot of salted water to boil. Cook spaghetti 2 minutes less than package directions for al dente. Reserve 1/2 cup pasta water, then drain.

Heat olive oil in a large skillet over medium heat. Add marinara and bring to a simmer. Stir in red pepper flakes if using. Add drained spaghetti and toss to coat, adding reserved pasta water a splash at a time until the sauce clings to the noodles. Cook 1-2 minutes more.

Divide spaghetti among the bread bowls, mounding slightly. Sprinkle remaining Parmesan over top. Return to oven for 5-7 minutes, just until the cheese melts and the bread edges re-crisp. Garnish with fresh basil and serve immediately.