Pre-heat the oven to 400°F.
Wash brussels sprouts and cauliflower.
Cut stems from brussels sprouts and cut into halves or quarters.
Cut the stem and leaves from cauliflower, then cut the florets from the head into 1-inch pieces for roasting.
Arrange the cauliflower and brussels sprouts on a baking sheet and drizzle with olive oil, tossing the vegetables to completely cover with oil and sprinkle with sliced garlic, salt, and pepper.
Place sheet pan in the oven and roast for 35 minutes, stirring halfway through to roast on all sides.
Remove pan from oven, arrange vegetables on a plate and serve as a side dish or as a salad topping.