In a large bowl, combine the soy sauce, mirin, brown sugar, Gochujang (Korean chile paste), ginger, garlic and sesame oil. Add the pork and toss well to coat. Try and make sure that almost all the pork is submerge in the sauce. Cover and place in the fridge for 1 hour or overnight.
Meanwhile, prepare the tomatillo sauce. Preheat the broiler to high. Line a baking sheet with parchment. Add the peeled tomatillos and place under the broiler for 3-5 minutes, turning once or twice or until the tomatillos are mostly charred all over. Remove from the oven and let cool slightly. Then add the charred tomatillos to a blender or food processor. To the blender, add the Gochujang, sesame oil, rice vinegar, soy sauce and lime juice. Blend until mostly smooth. Pour into a glass jar or serving bowl and then stir in the sesame seeds. Cover and store in the fridge until ready to serve. The sauce cane be store for at least a week in the fridge.
To make the slaw, preheat a grill or grill pan to high heat. Toss the spring onions, jalapenos and fresno chile with a little sesame oil. Grill the veggies until grill marks appear on both sides, about 5 minutes for the pepper and 3 minutes for the onions. Remove the veggies and allow to cool. Add the cabbage and mango to a mixing bowl. Chop the spring onions, de-seed the jalapeno + fresno pepper and then chop. Add the onions, peppers, cilantro, soy sauce, rice vinegar and any remaining sesame oil. Toss well. Store in the fridge until ready to serve.
Preheat the grill or a grill pan to medium high heat. Once hot, remove the pork from the marinade and grill until cooked through, about 4-5 minutes per side (depending on how thick or thin you cut your pork). As the pork is cooking, spoon the marinade of top for extra flavor. Allow the pork to rest at least 10 minutes and then thinly slice into strips. While the pork is resting, you can add the remaining marinade to a small saucepan and bring to a boil, reduce the heat and simmer 5 minutes or until slightly thickened.
To serve, add the sliced pork to a warmed taco shell. Top with slaw and tomatillo sauce. Add some cheese and sesame seeds. Serve with limes. DIG IN.