Cook ground beef, sausage, onions, and bell pepper in a large skillet or sauté pan over medium high heat, crumbling the meat with a wooden spoon as it cooks. Cook until beef and sausage are fully cooked and no longer pink (about 6 to 7 minutes). Drain off fat.
Add garlic and cook until fragrant (while stirring), about 30 seconds.
Stir in marinara sauce, tomato sauce, beef broth, Italian seasoning, salt, and pepper.
Add lasagna noodle pieces. Stir to combine and coat noodles with sauce mixture. Bring to a boil. Reduce heat as needed to maintain a strong simmer. Cover and simmer for 15 to 20 minutes or until noodles are tender. Stir occasionally to prevent noodles from sticking together.
Stir in the shredded mozzarella cheese until melted. Remove from heat and dollop with ricotta cheese, then sprinkle with Parmesan cheese.
Sprinkle with parsley when serving, if desired.