Preheat your oven to 375°F.
In a skillet over medium heat, brown the grass-fed ground beef until fully cooked, then drain any excess liquid.
In a medium bowl, whisk the egg and stir in the ricotta cheese, chopped baby spinach, garlic powder, and dried oregano until well combined.
Season both the cooked beef and the ricotta mixture with sea salt and black pepper.
Spread 2 tablespoons of the marinara sauce on the bottom of a small oven-safe baking dish.
Layer half of the noodles, half of the ricotta mixture, and half of the beef, then top with more marinara sauce.
Repeat the layers with the remaining noodles, ricotta, and beef, finishing with the rest of the marinara sauce.
Sprinkle the shredded mozzarella cheese evenly over the top.
Cover the dish with foil and bake for 25 minutes.
Remove the foil and bake for another 10 minutes until the cheese is melted and the edges are bubbling.
Let the lasagna rest for 10 minutes before serving to allow the layers to set.