- Preheat the oven to 180 ºC (350 ºF). In a saucepan, soften the spinach in the olive oil. Season with salt and pepper. Set aside.
- In a saucepan over medium heat, melt the butter. Add the flour and cook for 1 minute, stirring constantly. Add the milk and stir until it thickens. Add the cheese and nutmeg. Stir until the cheese has melted. Season with salt and pepper. Set aside.
- Cut the lasagna noodles in half crosswise. Cut fish into eight strips. Place a fish strip on the entire length of the noodle, fold the fish, as needed. Place 1/8th of the spinach at the beginning end of each lasagna. Roll up and place the rolls, seam side down, in a 38 x 25-cm (15 X 10-inch) baking dish, sprayed with oil. Cover with the sauce and cheese.
- Bake for about 25 minutes and finish cooking under the broiler to brown the cheese.