Cold sesame noodle salad is a picnic staple: springy noodles, a creamy sesame-peanut dressing, and crunchy vegetables that hold up well when made ahead and served cold.
Cook the noodles. Bring a large pot of salted water to a boil. Cook the noodles according to package directions until just tender (spaghetti usually 8–10 minutes; thinner Asian noodles often 4–6 minutes).
Rinse and cool properly. Drain in a colander, then immediately rinse under cold running water, tossing until completely cool. Shake off as much excess water as you can.
Toss with a bit of oil. Transfer cooled noodles to a large bowl and drizzle with about 1 tsp neutral oil (from the dressing oil) or a few drops of sesame oil; toss to lightly coat to prevent clumping.
Prep the vegetables. Cut cucumber and carrot into thin matchsticks and slice the scallions. If using bell pepper or cooked chicken/tofu, prep those as well.
Make the sesame-peanut dressing. In a medium bowl, whisk together peanut butter, tahini, soy sauce, rice vinegar, toasted sesame oil, remaining neutral oil, brown sugar or honey, garlic, ginger (if using), and chili crisp/oil or sriracha. Add cold water 1 tbsp at a time until smooth and pourable (like heavy cream).
Taste and adjust the dressing. Taste with a noodle or cucumber. If too salty, add a splash more water or a bit more sugar. If flat, add another teaspoon of vinegar or a pinch of salt.
Combine noodles and dressing. Pour about two-thirds of the dressing over the cooled noodles and toss until evenly coated. Add more dressing as needed so noodles are generously sauced but not swimming.
Fold in vegetables and protein. Add cucumber, carrot, scallions, sesame seeds, and bell pepper (if using). Fold in shredded chicken or tofu if using. Toss gently to distribute.
Chill for best texture. Cover and chill at least 30 minutes and up to 24 hours. If noodles seem tight or dry after chilling, loosen with a spoonful of water and a drizzle of sesame oil.
Finish and pack for the picnic. Right before serving, taste again; squeeze over lime and add more chili oil if desired. Adjust salt or vinegar if needed. Pack in a well-sealed container; keep lime wedges and extra chili oil separate if you want people to customize.