Bring a large pot of salted water to a boil. Cook ramen for 2 to 3 minutes. (If using spaghetti, cook until just al dente, about 8 minutes.) Drain and rinse under cold water.
In a large skillet, heat oil over high heat, add vegetables and stir-fry until just wilted, about 5 minutes.
In a large bowl, toss noodles with peanut sauce until well-coated. Add vegetables and shrimp and toss. Divide among 4 bowls and sprinkle each with scallions and sesame seeds. Serve at room temperature.