Place onion in a 5- to 6-quart slow cooker. Place half of the pork chops atop onions. Sprinkle with half of the Italian seasoning, garlic, salt, and pepper. Repeat layering with remaining pork chops, Italian seasoning, garlic, salt, and pepper. Top with tomatoes and balsamic vinegar. Add zucchini pieces to cooker.
Cover and cook on low-heat setting for 8 to 9 hours or on high-heat setting for 4 to 4-1/2 hours.
Using a slotted spoon and tongs, transfer meat and vegetables to a serving platter; cover and keep warm. In a medium saucepan stir together cornstarch and the cold water; stir in cooking juices from cooker. Cook and stir over medium heat until thickened and bubbly; cook and stir for 2 minutes more. Serve over meat and vegetables. Serve with orzo.