Peel and core the pumpkin and cut into bite-sized pieces. Halve the zucchini lengthways and cut into thick slices. Quarter the corn lengthways. Clean and quarter the mushrooms. Knock 2 Krachai fingers flat with a knife, cut 1 finger into thin slices.
Mix the ingredients for the paste with a little water with a hand blender to form a smooth paste.
Bring the broth to the boil in a large saucepan and add the paste. Then gradually add the vegetables. First the pumpkin, after a few minutes the zucchini, then krachai, chillies, mushrooms and corn. At the end, add the prawns to the soup and let them steep.
Season with fish sauce and possibly a little sugar, add Bai Maenglak and serve.