Preheat your oven to 375°F.
Cook the whole wheat lasagna noodles in boiling water according to package directions until al dente, then drain and set aside.
In a medium skillet over medium heat, add the olive oil and minced garlic, sautéing for 1 minute until fragrant.
Add the ground beef to the skillet, season with sea salt, black pepper, and dried oregano, and cook until browned and crumbled.
Pour the marinara sauce into the skillet with the beef, lower the heat, and simmer for 5 minutes.
In a small bowl, roughly chop the fresh baby spinach and stir it into the ricotta cheese until well combined.
In a small oven-safe baking dish, spread a spoonful of the meat sauce on the bottom, then layer with half a noodle (cut to fit), half of the ricotta-spinach mixture, and a portion of meat sauce.
Repeat the layers with the remaining noodles and ricotta mixture, finishing with the last of the meat sauce and a sprinkle of mozzarella cheese.
Bake for 15-20 minutes until the lasagna is heated through and the cheese is melted and golden.