Mix the marinade. In a bowl, stir together 2 tablespoons fish sauce, the soy sauce, oyster sauce, 1 tablespoon palm sugar, coconut milk, garlic, cilantro stems and white pepper until the sugar dissolves. Add the sliced pork and turn to coat. Let it sit at least 20 minutes at room temperature, or up to overnight in the fridge.
Make the nam jim jaew. Combine 3 tablespoons fish sauce, lime juice, 1 tablespoon palm sugar, toasted rice powder, chili flakes, shallot and scallion. Stir until the sugar dissolves and taste. It should read sharp, salty, a little sweet and hot. Adjust with more lime or chili as you like.
Heat a cast iron or heavy skillet over medium-high until it just starts to smoke, then add the oil. You want the pan hot so the pork chars instead of steaming. A grill pan or outdoor grill over high heat works the same way.
Lay the pork out in a single layer, working in two batches so the pan stays hot. Leave it undisturbed for about 2 minutes to build color, then flip and cook 1 to 2 minutes more until the edges are charred and the pork is just cooked through. Do not crowd the pan.
Rest the pork on a board for 3 minutes, then slice any larger pieces. Resting keeps the juices in instead of running out onto the rice.
Build the bowls. Divide the jasmine rice among four bowls, pile on the pork, and add cucumber, cilantro and mint and a lime wedge to each. Spoon some nam jim jaew over the pork and serve the rest on the side for dipping.