Note: Before starting to cook, be sure the pork, bell peppers and onion are all sliced and the sauce is ready to go. The cooking process for this stir-fry is fast so it's helpful to have everything prepped!
Place the thinly sliced pork tenderloin in a bowl, sprinkle with the cornstarch, salt and pepper and toss to evenly combine.
Open the can of pineapple and drain the juice into a measuring cup. Add the remaining sauce ingredients and stir to combine. Set aside.
Place a large non-stick skillet over medium-high heat. Add 2 tablespoons of oil and heat for a minute or so until hot and shimmering. Add ½ the pork tenderloin and cook in an even layer, not moving for 3-4 minutes until browned. Brown on the other side then transfer to a plate. Repeat with the remaining pork tenderloin adding more oil if needed.
After browning the pork tenderloin, add the peppers and onions to the now-empty skillet and cook until softened, about 2-3 minutes. Add the pork back to the pan along with the sauce and 1 cup of pineapple chunks. Cook until the sauce has thickened and everything is bubbly and hot.
Serve over hot rice with the remaining pineapple chunks on the side. Enjoy!