Serve this flavorful stir-fry alongside Grilled Lemongrass Chicken.
Cook beans and Chinese mustard in boiling water until bright green and crisp, 2 to 3 minutes. Cool in ice water; drain.
In a wok or a large nonstick skillet, heat oil over high heat. Add garlic and onions; cook, stirring, until they begin to brown, about 1 minute. Add beans, Chinese mustard, peppers, and oyster sauce; cook, stirring, until tender, about 2 minutes. Serve immediately with Grilled Lemongrass Chicken.