In a large skillet, cook the diced pork belly over medium heat until crispy and golden brown. Remove excess oil from the skillet, leaving about 1-2 tablespoons.

Add the chopped onions and minced garlic to the skillet and sauté until softened. Add the chopped chili peppers and cook for another minute.

Return the crispy pork belly to the skillet and mix everything together. Season with soy sauce and calamansi juice, then stir to combine. Remove the skillet from heat and let it cool slightly.

Once cooled, mix in the mayonnaise to add creaminess to the sisig. Warm up the tortillas or taco shells according to package instructions.

Assemble the sisig tacos by spooning the pork mixture onto each tortilla or taco shell. Top with your favorite toppings like chopped green onions, cilantro, radishes, tomatoes, and lettuce. Serve immediately with extra calamansi or lime wedges on the side.