Pre-sliced pork belly is available at Asian grocery stores. You can also ask a butcher to cut a 4-ounce piece of pork belly into long bacon-like strips or do it yourself. The ideal thickness for this dish is about 1/16 inch, but about 1/8 inch is fine, too. It helps to partially freeze the pork first and use a very sharp knife. To make okonomiyaki with shrimp, omit the pork belly and fold 1/2 pound of peeled, deveined and roughly chopped shrimp into the batter with the cabbage and scallions.