Rinse and trim pork loin as desired. Cut pork into about 1-inch cubes.
In a medium bowl, whisk together soy sauce, vinegar, and sugar. Whisk in the garlic and crushed red pepper.
Preparing For the Freezer:
Place cubed pork into a 1-quart freezer bag, remove air, and seal. Sauce goes into a 1-quart freezer bag too. Place the chopped onions and bell peppers into a 1-quart freezer bag as well. Then put each of the three quart freezer bags into a gallon-size bag, seal, and freeze. (Keep the oil and cornstarch on hand for when you decide to cook the meal.)
Prepare after Freezing:
Completely thaw in the refrigerator.
Pour off and discard any liquid from the bag of pork. Add 1 cup cornstarch to the bag; seal bag and shake to coat the meat.
In a large skillet, heat the oil over medium-high heat. Add pork and stir-fry until cooked, about 10 minutes. Add vegetables and sauce. Stir-fry until vegetables are tender and crisp. Serve with rice, if desired.
Double the recipe to make one meal for now and freeze one for later! Of course, this meal does not need to be frozen - just skip the freezer instruction part of the recipe.