Preheat your oven to 390°F (200°C). Grease a 11x7-inch baking dish.
If using traditional lasagne noodles place them into the bottom of the baking dish. Pour hot water over the noodles until they are covered and let them soak for 30 minutes, then drain and discard water.
In another saucepan heat up olive oil over medium temperature. Sauté the onions for 2-3 minutes until translucent. Add chopped garlic and cook for one more minute.
Add the tomatoes to the onions. Season with pepper, salt, oregano and a pinch of sugar. Let simmer for 15 minutes.
In a large saucepan, heat 1/4 cup (60ml) water over medium heat until simmering. Add fresh spinach leaves and cook for 3-4 minutes. If using frozen spinach cook for 10 minutes until warmed through.
In a medium bowl combine ricotta, egg, and grated parmesan cheese. Season with a little bit nutmeg, salt, and pepper to taste.
When the spinach is cooked and drain the spinach using a colander, then season with salt and pepper. Let it cool down for 2-3 minutes before adding it to the ricotta mixture.
Assemble lasagna: Put a few tablespoons tomato sauce into the bottom of the baking dish. Top with 4 lasagna noodles. Spread 1/3 of the ricotta-spinach mixture on top of the lasagne sheets. Top it with 1/4 of the tomato sauce. Sprinkle 1/4 of the grated mozzarella cheese on top and cover with 4 lasagne noodles. Repeat layering two more times and finish with a layer of pasta topped with the remaining tomato sauce. Top with remaining cheese.
Cover baking dish with aluminum foil and bake for 20 minutes then remove foil and bake for 20 more minutes until the cheese is browned.