In a medium saucepan of boiling salted water, cook the potatoes until tender, 12 to 20 minutes, depending on size; drain. When cool enough to handle, peel and slice.

In another saucepan of boiling salted water, cook the cauliflower until just tender, about 3 minutes. Remove with a slotted spoon and rinse under cold water; drain well.

In the same boiling water, repeat this process with the carrot, then the green beans, and finally the cabbage. (The jicama is not cooked.)

To make the dressing, in a medium saucepan, combine the coconut milk, peanut butter, garlic, sweet soy sauce, lemon juice, lemon zest, brown sugar, hot pepper, salt and 2 tablespoons of water. Bring to a boil over moderate heat, stirring frequently. Reduce the heat to moderately low and simmer until thickened, about 10 minutes. Keep warm over very low heat until ready to use.

Arrange the vegetables in layers in a large salad bowl. Scatter the scallions on top. Garnish with tomatoes. Pour the warm peanut butter sauce over all. Serve at room temperature.