Brown the Meat: In a large skillet over medium-high heat, cook the ground beef, Italian sausage and onions until no pink is visible. Break up the meat with a wooden spoon as it cooks to ensure even browning. Once fully cooked, drain off excess grease and season with onion powder, garlic powder, Italian seasoning, and salt & black pepper to taste.
Prepare the Soup Base: Add the seasoned meat mixture, chicken broth, and marinara sauce to the crockpot. Stir well to combine all ingredients. Cover and cook on low for 6-8 hours or high for 3-4 hours, allowing the flavors to meld together and develop.
Cook the Pasta: Once the soup base has finished cooking, add the broken lasagna sheets to the crockpot. Stir gently to incorporate the pasta into the hot liquid. Allow the lasagna sheets to cook for 30-45 minutes or until they reach al dente texture - tender but still with a slight firmness.
Add the Cheese: In the last five minutes of cooking, stir in the ricotta cheese until it's well incorporated into the soup, creating a creamy texture. When serving, sprinkle shredded mozzarella cheese on top of each portion, allowing it to melt slightly before enjoying.