Meanwhile, in a heavy pot, heat remaining 2 teaspoons oil over medium-high heat. Add remaining onion and cook, stirring often until soft, 3 minutes. Add curry paste and stir until fragrant, about 1 minute. Add coconut milk and 1 cup water and bring to a boil.Add sweet potato, cauliflower, salt and pepper. Reduce heat to medium, cover and simmer until vegetables are tender, 10-15 minutes.