Preheat oven to 350ºF. Line a baking sheet with foil.
Cook the chopped bacon in a large skillet until crisp, 5 to 7 minutes. Remove to paper towels to drain. Pour off all but 1 teaspoon of the fat.
Add the onion and cook until soft and golden, 4 to 6 minutes. Add the spinach, cover, and cook until wilted, 2 to 3 minutes, stirring spinach from bottom to top once or twice. Drain off any excess water and transfer the mixture to a mixing bowl.
Add beaten eggs, bacon, ricotta, 3 tablespoons of Parmesan, oregano, salt, pepper, and cayenne to the bowl. Stir gently until combined.
Cut out the tops of both Panera Bread Sourdough Bread Bowls as if making jack-o’-lanterns out of pumpkins. Remove bread from inside, leaving about a 1/2-inch shell of crust. Save or freeze the bread, including the top crust, for another use, such as bread crumbs or croutons. Place bread bowls on prepared baking sheet.
Scrape filling into bread bowls and sprinkle with remaining 3 tablespoons of Parmesan. Bake, without the top crust of bread, until filling is set and a toothpick inserted in the center comes out clean, 45 to 55 minutes. Let cool 10 minutes before serving. Using a serrated knife, cut each bowl into 3 wedges, like a peace sign.
Tip: The pork bacon can be easily swapped with turkey bacon. Or for a vegetarian dish, skip the bacon and heat 1 teaspoon of oil in the skillet for sautéing the onion.