Grind the garlic, ginger, orange zest and spring onions to a paste in a food processor. Add the honey, orange juice, soy sauce and oil, then blend again. Pour the mixture over the cubed chicken and leave to marinate for at least 1 hr, but preferably overnight. Toss in the mushrooms for the last half an hour so they take on some of the flavour, too.
Thread the chicken, tomatoes, mushrooms and peppers onto 20 wooden skewers, then cook on a griddle pan for 7-8 mins each side or until the chicken is thoroughly cooked and golden brown. Turn the kebabs frequently and baste with the marinade from time to time until evenly cooked. Arrange on a platter, scatter with chopped spring onion and eat with your fingers.