Pre-heat oven to 425°, and line baking sheet pan with parchment paper. Set aside.
In a large mixing bowl, add peppers, mushrooms, onion, and Brussel sprouts. Add in garlic powder, Italian seasoning, olive oil, Balsamic vinegar; gently toss to combine. Season to taste with salt & pepper.
Arrange seasoned vegetables on prepared sheet pan in a single layer without overcrowding.
Place baking sheet in pre-heated oven and roast for about 45 minutes, flipping half way through. Vegetables are done once they are tender and begin to caramelize.