Simply seasoned veggies are the perfect side: Both fennel and Brussels sprouts are packed with antioxidants and fiber, and get tender and subtly sweet when roasted.
Preheat oven to 350°F. Remove and reserve fennel fronds. Cut each fennel bulb in half lengthwise, and partially remove cores to help keep wedges intact. Cut each half into 4 wedges. Combine fennel, Brussels sprouts, garlic, olive oil, salt, and pepper in a large bowl; toss to coat.
Spread in an even layer on a large baking sheet lined with parchment paper. Roast, stirring halfway through, until vegetables are tender and browned in some spots, about 50 minutes. Remove from oven and garnish with reserved fennel fronds.
Vegetables can be cut and seasoned (step 1) up to 3 days in advance; store in an airtight container in refrigerator. Let stand at room temperature 15 minutes before baking.