Blend onions, garlic, lemongrass, ginger, and dried shrimps with ¼ cup (60ml) water into a smooth paste. Remove and pour into a small bowl. Mix in ground coriander, cumin, turmeric, and chili powder.
In a non-stick fry pan heat 1 tablespoon vegetable oil. Pan fry tofu until golden on all sides. Remove and set aside.
In a large pot, heat remaining 2 tablespoon vegetable oil. Add spice paste and fry for 5 to 6 minutes until fragrant. Stir constantly so that it will not burn.
Add coconut milk and ¾ cup (180ml) water. Bring to a boil.
Add pumpkin, cabbage, pan fried tofu, and salt. Bring it back up to a boil. Reduce heat to low, cover, and let it simmer for 5 minutes.
Add long beans, red chilies, and bean threads (if using). Allow it to cook for another 5 minutes.