Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in noodles and return to a boil. Cook until the pasta floats to the top, 1 to 2 minutes; drain.
Heat oil in a large skillet over medium-high heat; cook and stir onion and garlic for about 1 minute. Add broccoli and bell pepper; cook and stir until just tender, about 3 minutes. Stir in shrimp, water chestnuts, baby corn, bamboo shoots, oyster sauce, and red pepper flakes. Continue cooking until shrimp and vegetables are heated through, about 3 minutes more.