Preheat a grill to medium. Meanwhile, in a large bowl, combine the bell peppers, onion, 2 tablespoons olive oil, 3/4 teaspoon salt and 1/2 teaspoon black pepper.
Cut the pork into 1/3-inch-thick slices, then into quarters, trimming any excess fat. Transfer the meat to a food processor and pulse 5 times to grind the meat. Add the fennel seeds, crushed red pepper and 3/4 teaspoon salt and pulse 2 more times. Divide the mixture into quarters; form each mound into a 5-inch sausage link, then flatten into an oval patty about 1/3 inch thick.
Place a cooling rack on one side of the grill grate and lightly oil. Scatter the vegetables on the rack (saving any oil in the bowl); cover and cook for 5 minutes. Turn the vegetables with a spatula and tongs. Rub the sausage patties with the oil left in the bowl and add to the other side of the grill. Cover and cook, turning the patties about halfway through, until grill marks appear, the meat is cooked through and the vegetables are tender, about 7 minutes.
Transfer the patties to a plate. Transfer the vegetables to a large bowl and add the remaining 1 tablespoon olive oil and the vinegar; season to taste with salt and black pepper. Arrange half of the vegetables in the rolls and top each with a sausage patty and the remaining vegetables.