In a large bowl mix together the diced avocado, onions, cucumber, shrimp, and crabmeat and season with salt and pepper, to taste. In another bowl or a kitchen blender mix together the yogurt, ketchup, and lemon juice. When mixed thoroughly, slowly add the hot sauce, (not too much as it will over power the seafood).
To finish the dish, slowly add the dressing to the avocado mixture until slightly wet. Place 3 to 4 slices of tomato in the center of each serving plate, slightly separate just so the tomatoes touch.
Fill an ice cream scoop with the salad and place in the center of the tomatoes. Garnish with chopped chives and serve.