Cut the chicken into 2 inch cubes and thread on to oiled skewers. Arrange side by side in a flat dish. Make a paste with yogurt, garlic, salt and pepper and tandoori paste. Mix thoroughly and spread evenly across the chicken. Cover with plastic wrap and leave for 5 hours turning several times. Line a grill tray with aluminum foil and brush with vegan butter. Cook the kebabs until the surface is flecked with brown and the chicken tender, about 4 minutes on each side. Brush on additional vegan butter when the kebabs are half cooked to keep moist. Arrange on plates with white rice and sprinkle n garam masala.