Prepare the Ingredients: Begin by breaking the firm tofu into bite-sized pieces by hand for a more rustic texture. Slice the pork belly thinly, and chop the Asian chives into manageable lengths, setting everything aside for the cooking process.
Tofu First: In a large skillet or wok, heat the sesame oil over medium-high heat. Add the hand-broken tofu pieces to the hot oil. Stir-fry the tofu until it's lightly golden on all sides, about 4-5 minutes. Carefully remove the tofu from the pan and set it aside on a plate.
Cook the Pork: In the same skillet, add the sliced pork belly. Stir-fry until the pork is nearly cooked through and starts to brown, approximately 5-7 minutes. The pork will cook in the flavorful base left by the tofu, enriching its taste.
Combine Tofu and Pork: Once the pork is nearly done, reintroduce the cooked tofu to the skillet. Gently stir to combine, allowing the tofu to reheat and soak up the flavors from the pork and the pan.
Add the Chives: Toss the chopped Asian chives into the skillet, mixing them with the pork and tofu. The chives will wilt quickly, adding their unique garlicky flavor to the dish.
Sauce It Up: Drizzle the Mentsuyu and oyster sauce over the skillet contents. Stir everything well to ensure the ingredients are evenly coated in the sauce. Allow the mixture to cook for another 2-3 minutes, letting the sauce thicken and glaze the stir-fry.
Serve Hot: Once the sauce has thickened to your liking and everything is well-combined, remove the skillet from heat. Serve the stir-fry immediately, preferably over a bed of freshly steamed rice.
