Preheat your oven to 375°F and lightly grease a small individual-sized oven-safe baking dish.
In a skillet over medium heat, brown the ground beef until fully cooked, then drain any excess fat from the pan.
Season the beef with sea salt, black pepper, garlic powder, and dried oregano, then stir in the marinara sauce and simmer for 2 minutes.
In a small mixing bowl, combine the ricotta cheese, half of a beaten egg, and finely chopped fresh spinach until the mixture is smooth.
Spread a thin layer of the meat sauce at the bottom of the prepared baking dish, then place one lasagna noodle sheet on top.
Spread half of the ricotta-spinach mixture over the noodle, followed by a layer of meat sauce and the second noodle sheet.
Top with the remaining ricotta mixture and meat sauce, then sprinkle the shredded mozzarella cheese evenly over the top.
Cover the dish with foil and bake for 20 minutes, then remove the foil and bake for another 10 minutes until the cheese is melted and golden brown.