For the vinaigrette: In a large bowl, whisk together the vinegar, lime juice, fish sauce, soy sauce, peanut oil, and sesame oil. Add the papaya and onions and mix well. Add the cucumber, mint, basil, sugar, and white pepper and refrigerate covered in a non-reactive bowl for 2 hours to let the flavors marry. Will keep 24 hours covered, refrigerated.
For the tuna: Preheat a grill to high heat. Drizzle the tuna with oil and season with salt and pepper. Place the tuna on the grill and sear on each side for 30 seconds to 1 minute. The inside should be raw. Remove the tuna from the grill. Slice the tuna into 1/4-inch thick slices.
Serve the tuna with the vinaigrette.
Preheat a grill.
Peel and halve the papaya. Scoop out seeds, season with salt and chile oil. Grill for 2 minutes, or until grill marks appear and papaya softens. Dice when cool.