Beef and Sausage Meatballs

In a 5- to 6-quart slow cooker, whisk together the crushed tomatoes, tomato paste, 1/2 teaspoon oregano, and 1/4 teaspoon each salt and pepper. Stir in the onion, basil, and half the garlic. In a large bowl, combine the Parmesan, panko, remaining garlic, 1/2 teaspoon oregano, and 1/4 teaspoon each salt and pepper. Add the sausage and beef and gently mix to combine. Shape the meat mixture into 20 balls (about 1 1/2 inch each) and place on top of the tomato mixture. Cook, covered, until the meatballs are cooked through, 4 to 5 hours on high or 6 to 7 hours on low. Twenty minutes before serving, cook the spaghetti according to package directions. Toss with the meatballs and sauce and serve with additional basil and Parmesan, if desired.