Preheat your oven to 375°F (190°C).
Cook the whole wheat lasagna noodles in boiling water until al dente, then drain and set aside.
In a skillet over medium heat, sauté the diced onion and minced garlic in olive oil until they become translucent and fragrant.
Add the ground beef to the skillet, seasoning with sea salt, black pepper, and dried oregano, and cook until the beef is fully browned.
Stir the tomato puree into the beef mixture and let it simmer on low for about 5 minutes to meld the flavors.
In a small mixing bowl, stir together the part-skim ricotta cheese and the fresh baby spinach until well combined.
Spread a spoonful of the meat sauce onto the bottom of a small individual-sized baking dish.
Place one lasagna noodle over the sauce, then spread half of the ricotta-spinach mixture on top, followed by another layer of meat sauce.
Repeat the layers with the second noodle, the remaining ricotta mixture, and the rest of the meat sauce.
Sprinkle the parmesan cheese over the top and bake for 20 minutes until the sauce is bubbly and the cheese is golden.