Mix together all the marinade ingredients. Cut the tofu into 12 cubes and blanch in boiling water for 1 min. Drain and dry and place in the marinade for 2 hours, turning from time to time.
Slice squash, onions and red pepper into bite-sized chunks, add the mushrooms, oil, shoyu and mirin and bake slowly in the oven (gas mark7) until the vegetables become very sweet (45mins-1 hour) turning from time to time.
Cut the broccoli into flowerets and blanch in boiling water for 2-3 mins, keeping the bright green colour. Drain and cool in cold, salted water.
Place one piece of each type of vegetable and 1 piece of tofu onto each kebab stick.