If using tofu, preheat the oven to 350 °F and line a baking sheet with parchment paper.
Drain and cube the tofu (no need to press it) and spread it out on the parchment paper. Bake for 15-20 minutes, until golden brown around the edges.
Meanwhile, trim the ends off the green beans and chop into bite-sized pieces.
Stir all of the sauce ingredients together with the peanut butter in a small cup or dish, using a fork.
Place the green beans in a non-stick skillet with a tablespoon of water and cover with a lid. Steam, over medium heat for 2-3 minutes, until they are darkened in color but still have little bit of crunch.
Add the baked tofu or peanuts, sauce, and sesame oil to the pan and toss or stir to combine. Stir for a minute or two, until warmed and well coated. The goal is just to combine and warm everything, nothing really needs to cook.
Transfer to a plate, sprinkle with sesame seeds, and serve immediately.