For the stir-fry:.
Place the peanuts in a blender, and grind briefly until they form a coarse meal. Set aside.
Heat a medium-sized heavy skillet. Add 1 tablespoon of the oil, and the ginger and garlic. Sauté for a few minutes, then add the crushed peanuts and the lemon zest. Cook over medium-low heat for 10 to 15 minutes, stirring often, until the peanuts are lightly toasted. Remove from heat and set aside.
As the peanut mixture is cooking, heat a large, nonstick wok or deep skillet. Drizzle in a little oil. When it is very hot, add the tofu and 1/2 teaspoon salt. Cook over high heat for 10 to 15 minutes to let the water evaporate, stirring occasionally. Sprinkle with lemon juice, reduce the heat, and cook for a few minutes longer. Transfer the tofu to the pan containing the peanut mixture and set aside.
Scrape out the wok or skillet if necessary, and return to the heat. Let it get very hot, then add the remaining scant tablespoon of oil. When the oil is hot, add the green beans. (The pan should sizzle when they hit.) Stir-fry over high heat for about 5 minutes, then sprinkle with the remaining 1/2 teaspoon salt and a small amount of red pepper flakes.
Stir-fry just a few minutes longer, or until the beans are divinely tender-crisp (mostly crisp, but just tender enough). Add the peanut-tofu mixture and toss everything together. Serve right away, over rice.
For the peanut sauce:.
Combine peanut butter and water in a bowl; mash and mix until uniform. Add remaining ingredients, and stir until combined. Add a little more water it you prefer it thinner. Salt to taste. Serve warm or room temperature, drizzled over hot green beans.