In a pan, sauté the mixed vegetables with olive oil, salt, garlic, and onion until they become tender. Then, set them aside.

In a bowl, mix the egg with the ricotta cheese and spinach.

Spread a little tomato sauce at the bottom of a baking dish. Then, place a layer of lasagna sheets.

Spread the sautéed vegetables over the lasagna sheets, followed by half of the cheese and egg mixture.

Add another layer of lasagna sheets, then the remaining vegetables, and then the rest of the cheese and egg mixture.

Sprinkle the shredded mozzarella cheese on top.

Bake the dish in an oven preheated to 250°C (about 480°F) for 40 minutes, until the top is golden brown and the lasagna is cooked through.

For a final touch, you can broil the top for a few minutes to make it more golden. Serve the lasagna hot.