In a medium size bowl, sprinkle the cucumbers with some salt and sugar; toss to coat and set aside.
In another medium size bowl, combine the chicken, garlic, ginger, Szechuan peppercorns and Sriracha. In a large, deep skillet, heat the oil, two turns of the pan, over medium-high heat. Add the chicken mixture and cook, breaking it up with a spoon, until browned and cooked through, 8-10 minutes. Add the stock, 1 cup water, soy sauce and fish sauce. Stir, scraping up any browned bits. Bring to a low simmer; add the chard and scallions and stir until the chard is just wilted, about 2 minutes.
Meanwhile, in a large pot, cook the noodles, according to the package directions. Divide among bowls. Top with the chicken mixture and cucumbers and serve with the lime wedges.