Preheat your oven to 375°F (190°C).
In a skillet over medium heat, brown the ground beef until fully cooked, then season with sea salt, black pepper, and dried oregano.
Drain any excess fat from the skillet and stir in the marinara sauce, allowing it to simmer for 2 minutes.
In a small mixing bowl, stir together the part-skim ricotta cheese and finely chopped fresh baby spinach until well combined.
Cook the lasagna noodles in a pot of boiling water according to the package directions until al dente, then drain and set aside.
In a small, individual-sized baking dish, spread a thin layer of the meat sauce on the bottom.
Place half a lasagna noodle sheet over the sauce, followed by a layer of the ricotta-spinach mixture and more meat sauce.
Repeat the layering process twice more, finishing with the remaining meat sauce on top of the final noodle layer.
Sprinkle the shredded mozzarella cheese evenly over the top and bake for 20 minutes until the cheese is bubbly and golden.
Garnish with freshly chopped parsley and let cool for 5 minutes before serving.