In a bowl combine all of the ingredients for the mustard sauce. Mix to combine. Place in the refrigerator for at least 30 minutes to allow the flavors to meld.
Preheat your grill to 375°F. Clean and oil the grates.
In a bowl, toss the baby bell peppers with a drizzle of vegetable oil and a sprinkling of salt and pepper. In a separate bowl, do the same with the onion quarters.
Once the grill is up to heat, grill the peppers and onions. Cook for 5-7 minutes, and then flip. At this point add the sausages to the grill as well. Cook for another 5-7 minutes. Flip the peppers and sausages one last time, cook for a remaining 4-5 minutes.
Remove everything from the grill and plate, family style. Serve with the mustard sauce on the side.
Recipe Courtesy of Megan Mitchell