Steam sweet potato and potato for 10 minutes. Add pumpkin and continue to steam for 10 minutes. Dish out the steamed ingredients and put aside.
Heat 2 tablespoons oil in a nonstick saucepan. Add cumin seeds and fry till fragrant. Add onion and stir in chilli powder. Fry till fragrant. Add the steamed vegetables, then the seasoning. Stir-fry till mixture is dry and well mixed. Dish out and set aside.
Sift flour into a mixing bowl. Stir in salt and rub in margarine until it forms a sandy mixture. Add egg and water; knead into a dough. Cover with a damp tea towel and leave to rest for 15 minutes.
Divide dough into equal portions. Flatten each portion into a round. Spoon in enough filling. Fold into a half moon. Pinch the edges to seal the filling.
Deep-fry the puffs in medium hot oil till golden brown.