In the pot or slow-cooker, prepare the spaghetti sauce per directions.
Preheat the oven to 350° F/175° C.
In the medium mixing bowl, stir together the ricotta, eggs, and ¼ cup of the grated Parmesan.
Spread a ladle or two of the prepared sauce in the bottom of the baking dish. Lay down a row of 4 lasagna noodles, then add another layer of sauce. Layer on half the spinach and basil leaves, then spread on about ½ of the cheese mixture. It doesn’t have to look pretty, just make sure that it is evenly distributed, even if it’s in clumps.
Add 4 more noodles, then a couple more ladles of the sauce. Layer on the rest of the spinach and basil, then the rest of the ricotta mixture.
Add 4 more noodles, then more sauce. Sprinkle on the Parmesan and cover with foil. You might not use all of the sauce.
Bake in the preheated oven for 45 to 55 minutes. Remove the foil and sprinkle on the mozzarella cheese, then return to the oven for about 5 to 8 minutes, until the cheese is bubbly and golden brown. Remove from the oven and allow to sit for about 5 to 10 minutes before serving.