Preheat the oven to 425°F (220°C).

Heat olive oil in a large frying pan over medium-high heat.

Add chopped onion and cook until softened and lightly browned (about 5 minutes).

Add minced garlic and cook for 30 seconds until fragrant.

Add chopped broccoli, diced red pepper, and diced zucchini to the pan.

Cook, stirring occasionally, until vegetables are soft and starting to brown (about 10 minutes).

Stir in marinara sauce, balsamic vinegar, and oregano.

Season generously with sea salt and freshly ground pepper.

In a medium bowl, whisk together ricotta cheese, egg, sea salt, freshly ground pepper, and nutmeg.

Spread 1/2 cup of ricotta mixture in the bottom of an 8-inch-square baking dish.

Cover with half of the eggplant slices in a single layer.

Spread half of the marinara sauce mixture over the eggplant.

Top with half of the remaining ricotta mixture.

Sprinkle with half of the grated Parmigiano-Reggiano cheese.

Arrange the remaining eggplant strips in a layer.

Top with the remaining marinara sauce mixture and ricotta mixture.

Sprinkle the rest of the Parmigiano-Reggiano cheese on top.

Dot with the fresh mozzarella cheese.

Cover the baking dish with nonstick aluminum foil.

Bake in the preheated oven for 35 minutes.

Remove the foil and turn the oven to broil.

Broil the lasagna for 5 to 10 minutes, or until the top is brown and bubbly.

Remove the lasagna from the oven and let it rest for at least 5 minutes before serving.