In a bowl, toss the shrimp with cornstarch and salt until evenly coated.
Heat the vegetable oil in a large skillet over medium-high heat. Add the shrimp and cook for about 2-3 minutes until they turn pink. Remove the shrimp from the skillet and set aside.
In the same skillet, add the bell pepper, onion, and garlic. Sauté for about 3-4 minutes until the vegetables are tender.
In a small bowl, whisk together the ketchup, rice vinegar, brown sugar, soy sauce, and sesame oil. Pour the sauce into the skillet with the vegetables and stir to combine.
Add the pineapple chunks and cooked shrimp back into the skillet. Cook for an additional 2-3 minutes, stirring occasionally, until everything is heated through and the sauce is slightly thickened.
Serve the sweet and sour shrimp over cooked rice.