Heat the olive oil in a saucepan over medium heat. Add the ginger, garlic, lemongrass and chili and cook to soften, about 3 minutes. Add the coconut milk, and sugar and simmer until thickened, about 5 minutes. Stir in the lime juice and season with fish sauce, and salt and pepper. Cool to room temperature. Add coriander stems and puree using an immersion blender or blender.
For the pork tenderloin:
1) Put the pork on a platter and sprinkle all over with salt and pepper. Add the olive oil and lime juice and turn to coat the pork with the marinade. Cover with clingfilm and set aside in the refrigerator.
2) Preheat an outdoor gas or charcoal griddle. Blot some oil onto a thick square of paper towel and then carefully and quickly wipe the hot grates of the grill to make a non-stick surface. Put the pork on the griddle and cook, turning to brown all sides, until crusty on the outside and almost cooked through but still slightly pink in the center, 10 to 15 minutes. Remove from the griddle and let rest for a few minutes.
For the chili coconut-tomato salad:
1) Preheat the oven to 190 degrees C, gas mark 5. Spread the coconut out in a thin layer on a baking sheet and bake, shaking every now and then for even cooking, until lightly browned, about 10 minutes. Allow to cool.
2) In a big bowl, toss together the tomatoes, red onion, chili, coriander, mint, salt and pepper. Drizzle with olive oil and fold in the toasted coconut and scallions.
Slice the pork and add it to the bowl with the tomato salad. Pour over the chili-coconut sauce and toss it all together.