Fill a large bowl with water and add ice cubes. Cook noodles in boiling water until just tender, 2 to 4 minutes if fresh, about 6 minutes for dry (or according to package directions). Drain and transfer the noodles to the ice water. When the noodles are cold, drain well and transfer to a very large bowl. Set aside.
Meanwhile, whisk peanut butter, vinegar, sesame oil and Shaoxing (or sherry) in a bowl until smooth. Add scallions, cilantro, if using, soy sauce and hot sauce, and stir to blend.
If using baby romaine, half lengthwise, notch out the core, and cut crosswise into 1/2-inch pieces. If using regular romaine, remove the tougher outer leaves. Halve lengthwise, notch out the core, halve again, and cut crosswise into 1/2-inch pieces. You should have about 8 cups.
Add the lettuce, chicken, bell peppers and cucumber to the noodles. Add three-fourths of the dressing and toss to coat. Season with salt and pepper. Add the remaining dressing if desired.
Transfer the salad to a serving bowl. Serve garnished with sesame seeds.
Notes: Shao Hsing, or Shaoxing, is a seasoned rice wine. It is available at most Asian specialty markets and in the Asian section of some larger supermarkets. If unavailable, dry sherry is the best substitute.
Sambal oelek, a spicy blend of chiles, brown sugar and salt, and Sriracha, a Thai chile sauce, can be found in the Asian section of many large supermarkets and at Asian markets.
Look for toasted sesame seeds at the supermarket near other Asian ingredients. Or toast regular sesame seeds in a small dry skillet over low heat, stirring constantly, until golden and fragrant, about 2 minutes.
Tip: To quickly poach boneless, skinless chicken breasts, place in a large skillet or saucepan. Add lightly salted water (or chicken broth) to cover and bring to a boil. Cover, reduce heat to low and simmer gently until the chicken is cooked through and no longer pink in the middle, 10 to 20 minutes, depending on size.
To Make Ahead: Cover and refrigerate the salad for up to 1 day or prepare the dressing (Step 2), cover and refrigerate for up to 5 days; thin with a little water as needed.
