For the pistou, purée 2 ¾ cups spinach with the olive oil, garlic, and Parmesan in a food processor, adding more olive oil if the mixture is too thick. Salt the pistou to taste.
Combine the ricotta with the lemon juice and zest, then season with salt to taste. Beat the ricotta mixture for approximately 3 minutes until smooth.
Preheat the oven to 400 F and move the racks to the lower and middle levels.
Spread about ¼ cup pistou over the bottom of a 10-inch oven-proof skillet.
Top the pistou with 2 lasagna noodles, snapping a third one into pieces to fit the edges.
Cover the noodles with another ¼ cup of pistou, making sure to cover them entirely.
Spread about ⅓ of the ricotta mixture evenly over the pistou, then cover it with ⅓ of the shredded gouda.
Repeat layering the noodles, pistou, ricotta, and gouda until you have three layers.
Top the final layer with the remaining spinach, roughly chopped or torn.
Spread the reserved lemon pulp over the spinach.
Reduce the oven temperature to 375 F. Put the lasagna on the middle rack and place a baking sheet on the lower rack beneath it to catch any drippings.
Bake the lasagna for approximately 30 minutes or until it is hot and the cheese is bubbling.
Turn the oven to broil and leave the lasagna in the oven for another 2 to 3 minutes until the top is brown. Remove from oven.
Let the lasagna cool for 10 minutes before slicing.