Preheat the oven to 375°F (190°C). Cook the lasagna noodles according to package instructions until al dente. Drain and set aside to cool slightly.
In a large skillet over medium heat, add the ground beef and diced onion. Cook until the beef is browned and the onion is translucent, about 5-7 minutes. Add the minced garlic and cook for an additional minute.
Stir in the marinara sauce and Italian seasoning. Let it simmer for about 5 minutes. Season with salt and pepper to taste.
In a mixing bowl, combine the ricotta cheese, 1/2 cup of the mozzarella cheese, Parmesan cheese, egg, and a pinch of salt and pepper. Mix until well combined.
To assemble the mini lasagna cups, spray a muffin tin with cooking spray. Cut the lasagna noodles into squares that fit into the muffin cups. Place one noodle square in the bottom of each cup.
Add a spoonful of the meat sauce on top of the noodle, followed by a spoonful of the ricotta mixture. Repeat the layers, finishing with a noodle square and a final layer of meat sauce.
Sprinkle the remaining mozzarella cheese on top of each cup.
Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and golden. Let cool for 5 minutes before removing from the muffin tin.
Garnish with fresh basil leaves if desired and serve warm.