Peel the cucumber and blanch the green peppers. Remove ribs and seeds of peppers. Peel the onion, and take off the outer leaves of the cabbage. Wash and dice the green tomatoes.
Slice or shred the cucumber, green peppers, onion and cabbage as thin as you can, leaving them in separate piles or in bowls. Mix a sprinkle of salt with each vegetable and leave them for 1 hour.
Press out as much liquid as possible from the salted vegetables. Mix together and add diced tomatoes.
Mix the vinegar and ½cup water with ½teaspoon salt. Add pepper and sugar, and bring just to a boil. Remove from heat and cool.
When the dressing is cool, mix with the vegetables. Let the vegetables soak in the liquid for a few hours before serving.
For a relish that keeps, place the vegetables layer by layer in a 1-gallon jar with a wide mouth. Use the same liquid mixture, only use more of it, and cover the vegetables with liquid. Cover the jar tightly. You can keep this relish mixture in the refrigerator for quite a few months.