Preheat your oven to 375°F (190°C).
Bring a pot of salted water to a boil and cook the lasagna noodles until al dente, then drain and set aside.
Heat olive oil in a skillet over medium heat and sauté minced garlic for 1 minute until fragrant.
Add the ground beef to the skillet, seasoning with sea salt, black pepper, and dried oregano; cook until browned and crumbled.
Stir the tomato puree into the beef and simmer for 5 minutes to allow the flavors to meld.
In a small bowl, combine the ricotta cheese with finely chopped fresh spinach.
In a small individual baking dish, spread a thin layer of the meat sauce on the bottom.
Layer with a piece of lasagna noodle (cut to fit), followed by half of the ricotta-spinach mixture and more meat sauce.
Repeat the layers, finishing with a final noodle and the remaining meat sauce.
Sprinkle shredded mozzarella cheese over the top and bake for 15-20 minutes until the cheese is melted and bubbling.