Bring to a boil enough water to just cover the noodles. Once boiling, add noodles and cook according to package instructions. Once noodles are done, drain off all but about 1/2 tablespoon of the cooking water. Stir in the peanut butter, soy sauce, sesame oil, and Sriracha mixture. If needed, thin out the sauce with a little water. Salt to taste. Toss with shishito peppers and sprinkle with red pepper flakes.