Place your chopped Brussels sprouts, carrots, red onions and garlic on a baking sheet. Drizzle the olive oil and mix together with your hands until all the vegetables are lightly covered. Spread the vegetables out so they have room to breath. Sprinkle with salt and pepper to taste.
Bake on 425°F for 30 minutes until the vegetables are browned and slightly crisp on the edges. Serve immediately as a side or a main entree. Enjoy!