Dissolve beef bouillon cube in boiling water in a large bowl. Stir soy sauce, cornstarch, teriyaki sauce, and sugar into the water. Lay beef strips into the soy sauce mixture; stir to coat beef entirely.
Heat oil in a large skillet over medium-high heat. Cook and stir vegetables in hot oil briefly, about 1 minute. Stir water chestnuts into the vegetable mixture, place a cover over the skillet, and cook at a simmer until the vegetables are hot, about 5 minutes. Remove vegetable mixture with a slotted spoon to a large bowl, reserving juices in the skillet.
Pour beef with soy sauce marinade into the hot skillet; cook and stir until browned completely, about 5 minutes. Return vegetable mixture to the skillet; bring to a simmer. Cook and stir until completely hot, about 2 minutes.
