Heat the grill to medium. Halve the aubergine lengthways and cut a crisscross pattern into the cut side. Put cut-side down on a baking sheet and grill for 10 minutes, or until the skin starts to brown.
Turn over and spread 1 tbsp miso paste on each cut side, put back under the grill and cook for 15 minutes, or until the aubergine is soft and cooked through, being careful not to let it burn. Sprinkle with sesame seeds and grill briefly to brown them.
Meanwhile, soak the rice noodles following the packet instructions. Peel the cucumber, then use the peeler to cut into thin strips. Toss these with the noodles and season with salt and the vinegar.