Preheat your oven to 375°F and prepare a small individual-sized baking dish.
Bring a pot of water to a boil and cook the lasagna noodles until al dente, then drain and set aside.
In a medium skillet over medium-high heat, brown the ground beef with minced garlic, sea salt, and black pepper until no longer pink.
Add the fresh spinach to the skillet and sauté for 1-2 minutes until just wilted, then remove from heat.
In a small mixing bowl, whisk the egg and then fold in the ricotta cheese and dried oregano until well combined.
Spread 2 tablespoons of marinara sauce on the bottom of the baking dish to prevent sticking.
Place half of a noodle sheet (broken to fit) in the dish, followed by half of the beef and spinach mixture, half of the ricotta mixture, and a layer of sauce.
Repeat the layers once more, finishing with the final noodle piece, the remaining marinara, and a sprinkle of mozzarella cheese.
Cover the dish with foil and bake for 20 minutes; remove the foil and bake for another 10 minutes until the cheese is golden and the sauce is bubbling.
Allow the lasagna to rest for 5 minutes before serving to let the layers set.