Peel cucumber and slice in quarters lengthwise. Cut off seeds and slice cucumber diagonally into ¼ inch thick slices. Place in a bowl and sprinkle with salt. Set aside for 20 minutes.
Transfer drained cucumber and tomatoes to pre-soaked claypot.
Lightly sprinkle salt and pepper on both sides of salmon. Place salmon on cucumber and tomatoes.
Mix garlic chili sauce, vinegar, sugar in a small bowl. Pour over salmon. Drizzle a teaspoon of sesame oil onto salmon.
Cover claypot and put in a cold oven. Set oven temperature to 400°F (200°C) and cook for 40 minutes.
Remove from oven and spoon out excessive juices.
Drizzle with remaining teaspoon of sesame oil. Sprinkle with toasted sesame seeds and green onions.