Turn on your Spark and preheat to 500°F.
Make a pouch with a few layers of foil to hold the cabbage and onions. Alternatively, use a grill safe pan. Add a pinch of salt, the maple syrup, and vinegar. Seal the pouch and place on the grill with the lid closed. Check after about 20 minutes - it’s done when the cabbage is soft.
Add the peppers directly on the grill grates and roast until they’re soft and beginning to char. Rough chop the peppers.
Add the bratwurst to the grill and cook until the skin starts to split, about 10 minutes. Turn a few times during cooking for even grilling.
Toast your buns on the grill. Top them with the brats, cabbage and onions, and chopped bell peppers. Serve hot with whole grain mustard.