How to Make It
Using a 2 ¼-inch round cutter, cut 16 rounds from bread slices. Discard any remaining bread, or reserve for another use. Cut halloumi into ¼-inch-thick slabs. Using 2 ¼-inch cutter, cut 8 rounds from halloumi slices. Reserve remaining cheese for another use.
Toast bread rounds. Heat a grill pan over high. Grill cheese rounds until grill marks appear, about 2 minutes per side. Spread mayonnaise evenly on 1 side of each toasted bread round. On each of 8 bread rounds, layer 1 tomato slice, 1 grilled halloumi round, 2 arugula leaves, and 1 bacon piece. Cover with remaining bread rounds. Secure each sandwich with a wooden pick.