Combine the peanut butter, sesame oil, soy sauce, vinegar or lemon juice, hot water, garlic, ginger, red pepper/sriracha, and sugar in a small bowl and whisk well to combine. This can also be prepared in a blender or a food processor. If you need to adjust the consistency of the sauce so that it is thinner, add more hot water, 1 tablespoon at a time.
Bring a large pot of water to a rolling boil and salt it. Cook the soba noodles, according to package instructions (about 6 minutes). When the noodles are cooked, drain the noodles. Toss the noodles in the peanut sauce, along with the vegetables and chicken (if using).
Garnish with cilantro and sesame seeds. Serve warm or cool. If preparing as a cold salad, refrigerate and serve cold.
Spicy Peanut Sauce recipe adapted from my dear friend Olivia.Make it Gluten-Free: Check your soba noodle packaging. Some may contain wheat flour, so opt for soba noodles that are made with 100% buckwheat flour. Substitute soy sauce with tamari or liquid aminos.