Preheat the oven to 375°F and lightly grease a 9x13-inch baking dish.

Heat the olive oil in a large skillet or Dutch oven over medium heat. Add the diced onion and cook for 4 to 5 minutes until softened.

Stir in the minced garlic and cook for 30 seconds. Add the ground beef and cook until browned, breaking it up as it cooks.

Add the kosher salt, black pepper, dried oregano, dried basil, and red pepper flakes if using. Stir in the tomato paste and cook for 1 minute.

Add the marinara sauce, crushed tomatoes, and water. Stir well and simmer gently for 20 minutes, stirring occasionally, until slightly thickened.

In a medium bowl, combine the ricotta cheese, egg, grated Parmesan, parsley, salt, and black pepper. Mix until smooth.

Spread a thin layer of meat sauce in the bottom of the prepared baking dish. Arrange 3 lasagna noodles over the sauce.

Spread one-third of the ricotta mixture over the noodles. Top with one-third of the meat sauce and sprinkle with 1 cup of shredded mozzarella.

Add 3 more noodles, half of the remaining ricotta mixture, half of the remaining sauce, and another 1 cup mozzarella. Repeat one final time with the last 3 noodles, remaining ricotta mixture, remaining sauce, and final 1 cup mozzarella.

Sprinkle the top with the remaining 2 tablespoons grated Parmesan.

Cover loosely with foil and bake for 30 minutes.

Remove the foil and bake for 15 to 20 minutes more, until the cheese is melted, golden in spots, and the edges are bubbling.

Let the lasagna rest for 15 minutes before slicing. Garnish with fresh basil if desired and serve warm.