Preheat a cast iron skillet over medium heat on your campfire grate (or camp stove). Add the oil, then the onions, peppers, and salt. Cook for a few minutes until they just begin to soften, then add the bratwurst, nestling them into the vegetables so they come in contact with the skillet.
Turn the brats and stir the vegetables occasionally, until the brats are cooked through (internal temp of 160°F), 15–20 minutes.
Remove from the heat and divide the brats and veggies among the sandwich rolls.
Top with mustard and enjoy!
Crank up the spice with your choice of peppers. Bell peppers for no heat, poblano for moderate heat, jalapeños for high heat, or serrano peppers for extreme heat.Put the leftovers in a food storage container and place in a cooler overnight. Chop up in the brats and peppers in morning and mix with your eggs to make a delicious scramble.