For the tandoori sauce, peel and finely chop the garlic. Mix with yoghurt, mustard and honey. Season to taste with salt, pepper and cumin.
Oil the skewers. Clean, wash and cut the peppers, zucchini, radishes and fennel into large pieces. Peel and quarter onions. Put the vegetables alternately on the skewers. Spread all skewers with approx. 1⁄4 of the tandoori sauce and let them stand for approx. 1 hour.
Drain the skewers and place them in the grill trays. Grill on the hot grill for 10-15 minutes while turning. Add the rest of the tandoori sauce.