Preheat broiler. In a large bowl, combine first 7 ingredients; toss to coat. Transfer to a rimmed baking sheet. Broil 3-4 in. from heat until brown and crisp-tender, 12-15 minutes, turning once. Meanwhile, in a large skillet, heat olive oil over medium-high heat. Add onion; cook and stir until tender, 4-5 minutes. Add ginger, garlic, garam masala, curry powder and, if desired, cayenne pepper; cook 1 minute longer. Stir in tomatoes, coconut milk, salt and pepper. Bring to a boil; reduce heat. Simmer, uncovered, until thickened, 10-12 minutes, stirring occasionally. Stir in cauliflower; sprinkle with cilantro. If desired, serve with rice, naan and lime wedges.