How to Make It
Bring two medium saucepans of salted water to a boil. Add the potatoes to one of the pans and cook until tender, about 10 minutes. Remove with a slotted spoon and drain well. Meanwhile, cook the green beans in the other pan until tender, about 4 minutes. Remove with a slotted spoon and drain well. As a pan becomes available, cook the carrots and broccoli, separately, until just tender, about 4 minutes each. Drain the vegetables well.
Meanwhile, puree the peanut butter, garlic, red-pepper flakes, brown sugar, lemon juice, soy sauce, salt, and hot water in a blender. Put one of the empty saucepans over moderately low heat. Pour the sauce into the pan and warm through. Stir in the scallions and cilantro.
Pour a little sauce on one large platter or individual plates. Arrange all the vegetables in small piles over the sauce. Sprinkle with the seeds or nuts and serve with the remaining sauce.