Brown the meat:
In a skillet over medium heat, add olive oil and cook the ground beef (or sausage) with chopped onion until browned. Add garlic and cook for 1 minute. Drain excess fat.
Add ingredients to crockpot:
Transfer the cooked meat mixture to the slow cooker. Stir in crushed tomatoes, tomato sauce, broth, Italian seasoning, basil, red pepper flakes, salt, and pepper.
Slow cook:
Cover and cook on Low for 6–7 hours or High for 3–4 hours.
Add noodles:
About 30 minutes before serving, stir in the broken lasagna noodles. Cook until the noodles are tender.
(Optional: Use cheese tortellini instead for a creamy tortellini soup crockpot version.)
Prepare the cheese mixture:
In a small bowl, combine ricotta, mozzarella, and Parmesan cheese.
Serve:
Ladle the hot soup into bowls and top each with a spoonful of the cheese mixture. Garnish with fresh basil or parsley.