In a small saucepan, combine the broth, oyster sauce and soy sauce. Bring to a boil. Combine cornstarch and water until smooth; gradually stir into the pan. Bring to a boil; cook and stir until thickened, about 2 minutes. Set aside and keep warm., In a large skillet, saute shrimp, mushrooms, sprouts and onion in 1 tablespoon oil until shrimp turn pink and vegetables are crisp-tender, about 2 minutes. Remove from heat; cool slightly. In a large bowl, whisk egg whites and soy sauce. Stir in cooked shrimp mixture., In a large skillet, heat remaining oil. Drop shrimp mixture in batches by 1/3 cupfuls into oil. Cook until golden brown, 2-3 minutes on each side. Serve with sauce. If desired, sprinkle with black and white sesame seeds and additional green onions.