Preheat the oven to 375 degrees F. Cook the pancetta and about two-thirds of the bacon in a large skillet over medium heat, stirring occasionally, until crisp, about 10 minutes. Transfer the bacon and pancetta to a bowl using a slotted spoon. Reserve the drippings in the skillet.
Add the onion to the skillet and cook, stirring occasionally, until soft and golden, about 8 minutes. Add the ginger, garlic and chili powder and cook, stirring, 1 minute. Add the tomatoes and their juice, the molasses, Worcestershire sauce, vinegar, mustard powder, 1/2 teaspoon salt, and pepper to taste. Increase the heat to medium high, bring to a simmer and cook until slightly thickened, about 5 minutes. Add the pinto beans, then add the navy beans and their liquid and return to a simmer. Stir in the pancetta-bacon mixture. Transfer to a 2-quart baking dish.
Pulse the buns with the remaining uncooked bacon in a food processor until finely ground. Sprinkle the crumbs evenly over the bean mixture. Cover and bake 45 minutes, then uncover and bake until the crumbs are golden brown, about 20 more minutes.