Heat a large oven-safe skillet over medium heat. Add the olive oil, then the ground beef and chopped onion. Cook for 6 to 8 minutes, breaking up the meat, until the beef is browned and the onion is softened. Drain excess grease if needed.

Stir in the garlic, Italian seasoning, salt, black pepper, and red pepper flakes if using. Cook for about 30 seconds, until fragrant.

Add the marinara sauce, diced tomatoes, and water. Stir well and bring to a gentle simmer.

Add the broken lasagna noodles and stir so they are mostly submerged in the sauce. Reduce the heat to medium-low, cover, and cook for 15 to 18 minutes, stirring a few times, until the noodles are tender and the sauce has thickened slightly.

In a small bowl, mix the ricotta, 1 cup of the mozzarella, 2 tablespoons of the Parmesan, and the chopped parsley or basil.

Dollop the ricotta mixture over the cooked noodles in the skillet. Sprinkle the remaining 1 cup mozzarella and remaining Parmesan over the top.

Place the skillet under the broiler for 2 to 4 minutes until the cheese is melted and browned in spots, watching closely. Alternatively, cover the skillet on the stovetop for a few minutes until the cheese melts.

Let the skillet lasagna rest for 5 to 10 minutes. Garnish with extra chopped parsley or basil and serve warm.