Slice bell pepper (removing seeds and stem) and onion (root to tip). Toss with 1 Tablespoon vegetable or olive oil and salt and pepper. Place in zip top bag to use later at campground, or use immediately.
Set grill to medium low heat. Let the grill heat up for about 5 minutes. Put brats on one side of the grill, and the peppers and onions on the other (or use a skillet or aluminum foil if your grates are too big for the peppers). Cook everything 15-20 minutes, turning the brats frequently and stirring the peppers and onions occasionally.
Add buns to the grill (open face toward the flame) and toast for 2 minutes. Remove everything from grill and build your bratwurst masterpiece, topping with mustard, ketchup, peppers and onions, and sauerkraut, if desired. Dig in and enjoy!