Light a grill if using and oil grates. Pat pork dry and transfer to a cutting board. Using a sharp knife, cut pork lengthwise, slicing halfway through. Open up like a book and place between sheets of plastic wrap. Pound until uniformly 1/2-inch thick.  Rub with oil, 1/2 tsp chili powder, 1 tsp kosher salt and several grinds of pepper.

Peel onion and cut into 1/2-inch thick slices, keeping rings intact. Reserving 3/4 of the best slices for grilling, finely chop the remaining 1/4 sliced onion.  Peel and chop ginger. Squeeze 1/2 lime into a small bowl.  Cut remaining half into wedges.

Brush onion slices with oil and add to grill. Add pork to grill and cook over medium heat, turning once or twice, until onions are lightly charred and very tender and pork is lightly charred and cooked through, about 10 minutes. Transfer to a cutting board and loosely cover with foil to keep warm.

Brush tortillas lightly with oil and grill, turning once or twice until lightly charred, about 2 minutes.  Wrap in foil or a towel to keep warm.

To make peanut sauce, heat 1 tablespoon oil in a medium saucepan over medium-high.  Add ginger and chopped onion; cook until golden, 1-2 minutes. Add 1 teaspoon chili powder. Add coconut milk, 1 1/2 tsp sugar, 1/2 tsp salt, and 1/4 cup water; simmer until slightly reduced, about 5 minutes.  Whisk in peanut butter and 1 tbsp lime juice; transfer to a bowl.

Coarsely chop grilled onions. Trim ends from cucumber then thinly slice.  Transfer both to a bowl and stir in remaining lime juice, 1 tbsp oil, and a pinch each salt and pepper.  Cut pork crosswise into 1/2-inch slices. Serve pork with salad, tortillas, peanut sauce and lime wedges.