Bring 2 pots of water—1 large and 1 medium—to a boil and salt them. Halve the lotus root lengthwise and slice crosswise into half-moons about 1/4 inch thick. When the smaller pot boils, add the lotus and cook, stirring occasionally until it’s tender, 4 to 6 minutes. Drain, rinse under running water, and drain again.
When the large pot boils, add the noodles and cook, stirring occasionally, for 5 minutes, then start tasting. (If using fresh, check after a minute.) When the noodles are tender but still have some bite, scoop out about 1 cup cooking water, then drain the noodles; run the noodles under cold water and drain again.
Cut the tofu crosswise into about 12 slices; stack the slices and cut them into thin ribbons no more than 1/2 inch wide.
Return the large pot to medium heat. When it’s dry and hot, add the vegetable oil, swirl, then scatter in the tofu and sprinkle with salt and pepper. Cook, undisturbed, until the pieces have browned on one side and release easily, 5 to 10 minutes. Transfer the tofu to a plate, leaving as much oil in the pot as possible.
Add a little more oil to the pot if it looks dry and turn the heat to medium-high heat. Add the onion, garlic, and ginger and cook, stirring, for about 1 minute. Add the greens and sprinkle with salt and pepper. Cook, stirring occasionally, until the vegetables soften, 3 to 5 minutes, depending on the type; add reserved cooking water as necessary to keep them from sticking. Add the soy sauce, sesame oil, and red chile flakes.
Add the tofu and lotus to the pan and stir to com- bine. Add the noodles and toss with tongs, adding more reserved cooking water to make a smooth sauce. Taste and adjust the seasoning. Serve garnished with the cashews.