MIX tomatoes and tomato paste in slow cooker until blended. Stir in vegetables.
CUT meat into 8 pieces; pound to 1/2-inch thickness. Sprinkle with oregano. Add to slow cooker; press into sauce with back of spoon. Cover with lid; cook on LOW 4 to 4-1/2 hrs. (or on HIGH 2-1/2 to 3 hours).
COOK pasta as directed on package, omitting salt. Transfer meat to plate, reserving sauce in slow cooker; cover meat to keep warm. Mix cornstarch and water until well blended. Add to sauce; stir. Cook, covered, on HIGH 6 to 8 min. or until thickened.
DRAIN pasta; spoon onto serving plates. Top with meat, sauce and cheeses.