Preheat a panini grill or a heavy-bottomed pan over medium heat.
Cut the foccacia into 4 equal sections, then split each section in half so it opens up like a sandwich. Stuff the foccacia with any combination of your favorite pizza toppings.
Place panini in sandwich press. If using a pan on the stovetop, place another heavy skillet or a brick wrapped in foil on top of the sandwiches to press them down. Press until cheese is melted and bread is crisp on both sides, about 2-3 minutes on each side.