Place noodles in a bowl and pour in enough boiling water to cover; soak until noodles are softened, about 10 minutes. Drain.
Mix 1 cup water, chicken bouillon, and soy sauce in a bowl until sauce is smooth.
Heat olive oil in a large skillet over medium heat; cook and stir mushrooms, baby cabbage, mustard greens, lettuce, and Japanese cucumber until mushrooms are fragrant and vegetables are tender, about 5 minutes. Add noodles and sauce; cook and stir using a long wooden chopstick until sauce has nearly evaporated, about 5 minutes.
