Put the onion, chilli, garlic and shrimp paste in a food processor and process to a paste, or grind to a paste using a mortar and pestle. (Don't overmix or the onion will become too wet.)
Heat the coriander and cumin seeds in a small frying pan on the hob until they start to release their aroma. Grind in a pestle and mortar. Put the minced beef in a mixing bowl and add the onion mixture, toasted coriander and cumin seeds, soy sauce, sugar and lemon juice. Add the beaten egg and mix until evenly combined. (This is best done with your hands.)
Shape the mixture into balls, each about the size of a golf ball. Lightly oil a shallow roasting tin or ovenproof dish and add the meatballs. Place on the upper rack of the halogen oven.
Set the temperature to 200°C (392°F) and grill the meatballs for 15–20 minutes until cooked through. Serve with noodles and a sweet dipping sauce, garnished with finely sliced spring onions.