Preheat oven to 400F. Line two cookie sheets with parchment paper.
Trim, cut, and rinse Brussels Sprouts. Drain sprouts on paper towel. Chop Sweet Bell Peppers and Onions. Set aside.
In a very large mixing bowl, whisk together the reduced Balsamic Vinegar, Dijon Mustard, and Spices. Add the veggies to the bowl and mix until all veggies are coated. Place balsamic coated veggies on the parchment lined cookie sheets, single layered.
Roast in the oven for 35 minutes. Remove from oven. Toss the veggies. Return to oven and roast another 10 minutes. Remove from oven and serve! Don’t worry about any of the blackened pieces. They are the best parts!
Taste even better the next day “cold” straight from the fridge!