To Make Sauce: Bring water to a boil in a large saucepan; dissolve bouillon cubes in boiling water. Remove 1 cup of this broth and mix with cornstarch in a small bowl, then return mixture to saucepan and let thicken. Stir in sugar, oyster sauce and soy sauce; cover, remove from heat and set aside.
To Make Chicken Nuggets: In a shallow dish or bowl, flour cubed chicken well and let stand in flour for 15 minutes. In a small bowl, beat egg, milk, salt and pepper together. Remove chicken from flour, dip in egg mixture, roll in flour again and deep fry in a large skillet or deep fryer until golden brown.
Place prepared chicken nuggets on a platter; heat sauce over low heat to heat through, then pour over chicken. Sprinkle cashew halves and green onion on top and serve.