Heat oil in a skillet. Add onion and sauté over medium-high heat for 3-4 minutes until golden brown. Add broccoli and cauliflower, fry for about 1-2 minutes.
Add curry paste and fry for about 30 seconds. Add coconut milk, fish sauce, brown sugar, and salt to the skillet. Bring to a boil, reduce heat, cook until vegetables are soft, about 3-4 minutes.
Meanwhile, heat another skillet over medium heat. Pour the nuts into the pan and fry until slightly brown, about 2-3 minutes. Pour the roasted nuts into the pan with vegetables, stir and serve, garnished with cilantro.