Marinate the chicken cubes with oil barbecue sauce, black pepper powder, salt, chilli sauce, and lemon juice. Mix well and let it rest for sometime. On a skewer, thread olive, onion shells, marinated chicken cubes, green bell pepper, red bell pepper, yellow bell pepper, and tomato. Heat a grilling pan and add oil. Grill the shashliks evenly on all sides. In the serving plate, arrange the halved cabbage head and arrange the skewers at the centre by pricking them into the cabbage.