Make the sweet and sour sauce by adding apple cider vinegar, brown sugar, ketchup, soy sauce, pineapple juice, and corn starch to a small saucepan and then heat until the sauce thickens and comes to a boil. Turn off the sauce and set it aside.
Make the stir-fry
Wash and chop the veggies of choice into bite-size pieces.
Saute the vegetables in oil for about 3 minutes over medium-high heat until they start to get bright in color.
Toss in the cubed pineapple and sprinkle with salt, then saute for another 3-5 minutes until the veggies are tender, but not too soft, and turn off the heat.
Pour the sweet and sour sauce over the stir-fry.
Fry the Tofu
Begin heating the frying oil while you prepare the tofu
Press the tofu to get out any excess liquid and then cut into small cubes.
Place corn starch and salt in a medium-sized bowl and give it a stir. Then toss in the cubes of tofu and shake the bowl until the tofu is coated with the corn starch.
Deep fry the tofu at 370 degrees F (190 C) for about 4 minutes until crispy and drain on a plate lined with a paper towel. (Check out my post on how to make perfect crispy fried tofu for more detailed instructions if needed.)
Add the tofu to the stir-fry and mix together and serve over cooked rice.
Notes
If you are making deep-fried tofu, add it just before serving to keep it crispy. If it sits with sauce on it, it will start to get soggy.
You can adjust the amount of sugar in the sweet and sour sauce to suit your taste. (This recipe is not as sweet as most store-bought brands, but still sweet enough to have a nice flavor that even kids will like.