Mix the Sauce - Whisk together the tamari, mirin, and chili garlic sauce. Set aside.
Prep the veg - Wash, destem, and destring the beans, if necessary. Cut the beans into 2-inch pieces. Dice the onion. Slice the garlic and chop the ginger. Thinly slice the serrano pepper after removing the stem, then shake out the seeds, and set aside.
Brown the Pork - Add the pork to a hot pan and stir-fry until it's browned and has some crispy edges. Remove from the pan and set aside. Wipe out the skillet with a paper towel.
Char the beans - Add your beans to the hot skillet and do not touch them for two minutes. Toss them, and continue to char the beans for another two minutes.
Sweat the aromatics - Add the grapeseed oil. Then add the onions, garlic, and ginger. Cook until they begin to soften.
Finish - Add the pork back to the pan. Stir in the sauce and the peppercorns.
Garnish and Serve - Once the sauce is heated through, you're finished. Remove from the heat, garnish with the serrano slices, and serve with rice.