In a small bowl, mix harissa, soy sauce, vegetable oil, and fresh cracked pepper. Reserve 2 tablespoons of marinade in the fridge.
Place pork belly in a gallon-size freezer bag, pour marinade over, and toss carefully to cover. Seal bag and refrigerate for at least 1 hour.
Heat grill to medium-high heat. In the meantime, slide pieces of pork onto skewers, alternating with cherry tomatoes.
Place skewers near middle of the grill. Cook, turning skewers and basting with reserved marinade every few minutes, until the pork belly is cooked through and browned on the outside, about 13 to 14 minutes. Serve immediately.