Preheat your oven to 375°F (190°C).
Boil the lasagna noodle in salted water until al dente, then drain and set aside on a non-stick surface.
Heat the olive oil in a small skillet over medium heat and sauté the diced yellow onion and minced garlic until translucent.
Add the ground beef, sea salt, and black pepper to the skillet, cooking until the meat is fully browned and crumbled.
Stir in the marinara sauce and chopped fresh spinach, simmering for 3-5 minutes until the spinach is wilted.
In a small mixing bowl, whisk the half egg and combine it thoroughly with the ricotta cheese and dried oregano.
In a small individual-sized baking dish, spread a thin layer of the meat sauce on the bottom.
Cut the cooked lasagna noodle into pieces that fit your dish, then layer noodle, ricotta mixture, and meat sauce.
Repeat the layers until all ingredients are used, finishing with a final layer of meat sauce.
Sprinkle the shredded mozzarella cheese evenly over the top.
Bake for 20-25 minutes until the sauce is bubbling and the cheese has turned a light golden brown.