Stir together 2 teaspoons cornstarch and 1 1/2 tablespoons soy sauce in a medium bowl until smooth. Add pork, tossing to coat. Let stand 15 minutes.
Prepare rice according to package directions. Keep warm.
Stir together remaining 2 teaspoons cornstarch, remaining 4 tablespoons soy sauce, 1/4 cup water, and 4 teaspoons hoisin sauce.
Heat oils in a large skillet or wok over medium-high heat 2 minutes. Add pork mixture, and stir-fry 3 to 4 minutes or until pork is browned. Add mushrooms and next 5 ingredients; stir-fry 2 minutes. Stir in hoisin sauce mixture, and stir-fry 1 minute or until thickened. Stir in orange juice. Serve over warm rice. Garnish, if desired.