In a large mixing bowl, combine the rinsed kidney beans, white beans, and Bush's Original baked beans. In a separate small bowl, whisk together the brown sugar, paprika, dry mustard, and freshly ground black pepper to create an even spice blend. Pour the barbecue sauce over the beans, then add the spice mixture and stir everything together until well combined and all beans are evenly coated. I like to taste a spoonful at this stage to adjust the seasoning—you can add a touch more paprika or brown sugar depending on your preference for smokiness or sweetness.

Transfer the bean mixture from Step 1 into a cast-iron skillet, disposable aluminum pan, or other grill-safe baking pan, making sure it's no more than three-quarters full. Cover the pan tightly with aluminum foil or a grill-safe lid to trap heat and moisture. While preparing the pan, preheat your grill to 350°F using medium heat. I find that covering the pan prevents the beans from drying out on the grill and ensures they heat evenly throughout.

Carefully place the covered pan on the grill grate and let it cook for 15-20 minutes, until the beans are heated through and the edges just begin to bubble slightly. Stir the beans halfway through cooking to ensure even heating, then remove from the grill and let rest for 2-3 minutes before serving. The beans will continue to warm slightly after you remove them from heat.