Prepare two saucepans of salted water and bring to a boil.

Boil potatoes in one saucepan for approximately 10 minutes or until tender. Drain.

Boil green beans in the other saucepan for approximately 4 minutes or until tender. Drain.

Separately boil carrots and broccoli until just tender, about 4 minutes each. Drain.

In a blender, combine peanut butter, crushed garlic, red-pepper flakes, brown sugar, lemon juice, soy sauce, salt, and hot water. Puree until smooth.

Pour the blended sauce into one of the empty saucepans and warm over moderately low heat.

Stir in chopped scallions and cilantro into the sauce.

Arrange boiled vegetables on a large platter or individual plates.

Drizzle a portion of the sauce over the vegetables and sprinkle with sunflower seeds or chopped peanuts.

Serve with the remaining sauce.