Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Slice the zucchini into thin rounds and the mushrooms into slices; spread them on the baking sheet, mist lightly with oil, and roast for 12-15 minutes until tender.
While vegetables roast, boil the lasagna noodle in salted water according to package directions until al dente, then drain and set aside.
In a small bowl, whisk together the ricotta cheese, egg, minced garlic, dried oregano, salt, and pepper until smooth.
In a separate bowl, stir the cooked lentils into the marinara sauce to create a high-protein meatless sauce.
In a small individual-sized baking dish, spread a spoonful of the lentil-marinara on the bottom.
Layer half of the lasagna noodle (cut to fit), followed by half of the ricotta mixture, half of the roasted vegetables, and a handful of fresh spinach.
Repeat the layers with the remaining noodle, ricotta, vegetables, and spinach, ending with a final layer of lentil-marinara.
Top the lasagna with the mozzarella and parmesan cheeses.
Bake for 20-25 minutes until the cheese is melted and the sauce is bubbling around the edges.
Let the lasagna rest for 5 minutes before serving to allow the layers to set.