Preheat oven to 425°F. In a large bowl toss together cauliflower, onion, oil, crushed red pepper and salt. Spread the mixture in a shallow metal roasting pan. Bake 25 minutes or just until the cauliflower is tender.
Meanwhile, rinse shrimp; pat dry. In a medium bowl combine shrimp, tomatoes, garlic and lemon zest. Pour shrimp mixture over cauliflower mixture. Bake 15 minutes more or until shrimp are opaque.
Combine cheese and dill; sprinkle over shrimp mixture. If desired, serve with lemon wedges.