1. Cook pasta according to package directions. During last minute of cooking time add asparagus. Drain in a colander and rinse with cold water until pasta and asparagus are cool. Transfer to a large serving bowl and set aside. If preparing a day ahead, bring to room temperature before serving.
2. Meanwhile, combine peanut butter, vinegar, soy sauce, sesame oil, brown sugar, garlic, ginger, and red pepper flakes in a small bowl. Add hot water and stir until sauce is smooth, breaking up any small clumps.
3. Add shrimp, red pepper, green onions, and 1/4 cup of the cilantro to the pasta. Add sauce and toss to combine. Sprinkle with remaining cilantro and sesame seeds. Makes 4 to 6 servings.