Soak 16 bamboo skewers in cold water (to prevent them from burning under the grill). Blanch the baby corn in a saucepan of lightly salted, boiling water for 2 minutes, then drain. Cut the capsicum into 2 1/2 cm chunks. Cut six of the spring onions into 4cm lengths. Thread the vegetables onto half of the skewers, alternating the corn with the capsicum and onion. Set aside. Preheat a hot grill.
Chop the remaining spring onions and put in a food processor bowl with the chicken, egg white, ginger, garlic, coriander, fish sauce and lemongrass. Process until chopped and beginning to bind together, but not completely smooth.
Divide the mixture into eight and use your hands to shape each piece around the remaining skewers. Arrange on a foil-lined grill tray. Mix the vegetable and sesame oils and lightly brush onto the chicken and vegetable skewers. Add the sesame seeds to any remaining oil.
Grill the chicken skewers for 15–20 minutes, turning occasionally, until golden. After 10 minutes, add the vegetable skewers and cook for 10 minutes, turning occasionally, until tender and golden. Brush over the remaining oil with the seeds for the last minute of cooking. Serve with sweet chilli sauce for dipping.
To prepare ahead, make up the mixture for the chicken skewers, then cover with plastic wrap. Keep chilled and cook within 2 days.