Place cornstarch in a large resealable plastic bag. Add pork, a few pieces at a time, and shake to coat. In a large skillet, cook the pork, peppers and onion in oil over medium heat until pork is no longer pink and vegetables are tender. Stir in salsa; heat through.
Place about 3/4 cup filling down the center of each tortilla; top with shredded cheese and sour cream. Fold in sides of tortillas.