Place the sun-dried tomatoes in a bowl with the boiling water, and allow to sit 10 minutes. Remove tomatoes with a slotted spoon, and coarsely chop. Reserve the water.

Transfer the reserved sun-dried tomato water to a saucepan, and bring to a boil. Place the chopped sun-dried tomatoes, zucchini, squash, and onion in a steamer basket, and set over the boiling water. Reduce heat to low, cover, and simmer 15 minutes, or until vegetables are tender. Discard water.

Transfer the steamed vegetables to a bowl, and mix with butter, sugar, pepper, and salt to serve.