Slice the liempo (pork belly) lengthwise - about 2cm (3/4 in) wide or have it sliced in the supermarket where you bought it to have a perfect pork belly cut.
Combine garlic, Sprite/7-up, vinegar, sugar, and pepper in a bowl. Pour over liempo (pork belly). Cover and marinate 3 to 4 hours in the refrigerator.
When ready to cook, drain the pork and discard marinade. Heat grill to medium and grill pork until thoroughly cooked, about 15 to 20 minutes on the first side and 10 minutes on the other. Make sure that the pork is not burnt.
To make the Vinegar-Soy Dip; combine onion, vinegar, soy sauce and pepper in a bowl. Stir well to blend. If you wish to have a spicier dip, add the sliced chili according to your preferred amount.
Serve the grilled liempo (pork belly) with the dip and cooked white rice.