Heat oven to 425ºF. Place a 2-foot long piece of heavy duty aluminum foil on counter. Turn edges up about 2 inches on all sides.
Place cauliflower in center of foil; arrange sausage around the cauliflower. Add olives, tomatoes and thyme sprigs. Drizzle with vinaigrette.
Fold edges of foil around sausage and vegetables forming a sealed pouch; place on baking sheet. Bake at 425ºF. for 35 minutes until cauliflower is tender.