1. Preheat oven to 425 degrees.
2. Cut potatoes into ¼ by ½ inch slices. Cut peppers, onions, and apple into 1 inch slices. Transfer vegetables and apples to a medium mixing bowl. Next, mince garlic and rosemary and transfer to mixing bowl.
3. Add olive oil and salt to mixing bowl, toss vegetables and apples to coat in spices and oil. Transfer to 2 baking sheets. Add 4 sausages, and spread everything out so it’s in one layer.
4. Bake for 15-20 minutes. Flipping sausages, vegetables, and apples halfway through. Sausages may split, if they do, keep split side down. Remove when potatoes are soft inside and crispy and browned on the outside.
5. Place each sausage on a bun, add desired amount of peppers, onions, and apples to sausage. Top with BBQ sauce and serve with potatoes.