Preheat your oven to 375°F (190°C).
In a skillet over medium heat, brown the ground beef with minced garlic, sea salt, and black pepper until fully cooked.
Stir the marinara sauce into the cooked beef and let it simmer on low for 5 minutes to meld the flavors.
In a small mixing bowl, combine the ricotta cheese, egg, and dried oregano until the mixture is smooth.
Cook the whole wheat lasagna noodles in boiling water according to package directions, then drain and pat dry.
In a small individual baking dish, spread a thin layer of the meat sauce on the bottom.
Layer with a portion of the noodles, half of the ricotta mixture, and half of the fresh spinach.
Repeat the layers with the remaining noodles, ricotta, and spinach, then top with the remaining meat sauce.
Sprinkle the mozzarella cheese evenly over the top layer.
Bake for 20-25 minutes until the cheese is melted and the edges are bubbling.
Let the lasagna rest for 5 minutes before serving to allow the layers to set.