Preheat your oven to 375°F and lightly grease a small individual-sized baking dish.
Boil the whole wheat lasagna noodles in a pot of salted water until al dente, then drain and set aside on a non-stick surface.
In a small skillet, heat the olive oil over medium heat and sauté the minced onion and garlic until fragrant and translucent.
Add the ground beef to the skillet along with the sea salt, black pepper, and dried oregano, browning the meat until it is fully cooked through.
Pour the tomato sauce into the skillet with the beef, stirring to combine, and let it simmer on low for about 5 minutes.
In a small bowl, whisk the egg and then measure out half; mix it with the ricotta cheese and the finely chopped fresh baby spinach.
Spread a small spoonful of the meat sauce on the bottom of the baking dish, then top with one noodle sheet (trimmed to fit if necessary).
Spread half of the ricotta mixture over the noodle, followed by half of the remaining meat sauce.
Add the second noodle sheet, the rest of the ricotta mixture, and the remaining meat sauce.
Top the lasagna with the shredded mozzarella cheese and bake for 20-25 minutes until the cheese is melted and bubbly.