Start by making the basil pesto. In a food processor, combine the fresh basil leaves, minced garlic, salt, and black pepper. While processing, slowly drizzle in the olive oil until the mixture becomes a smooth, vibrant green pesto. Set this aside to let the flavors meld.
Bring a large pot of salted water to a boil. Add the lasagna noodles and cook according to package instructions until al dente. Drain and lay the noodles flat on a clean kitchen towel or parchment paper to prevent sticking.
Using a sharp knife or mandoline, thinly slice the summer squash into rounds or lengthwise strips. This will ensure they layer nicely and cook evenly in the lasagna.
In a medium bowl, combine the ricotta cheese with half of the grated Parmesan cheese and about 3/4 cup of the prepared pesto. Mix well until creamy and well incorporated.
Preheat your oven to 375°F (190°C). In a 9x13 inch baking dish, spread a thin layer of marinara sauce on the bottom. Lay 3 cooked lasagna noodles over the sauce. Spread one-third of the ricotta-pesto mixture over the noodles. Arrange a layer of summer squash slices on top, then drizzle a few spoonfuls of marinara sauce over the squash. Repeat this layering process two more times: noodles, ricotta mixture, squash, and marinara sauce.
Once all layers are assembled, sprinkle the remaining Parmesan cheese and shredded mozzarella evenly over the top. Cover the dish with foil and bake for 25 minutes. Remove the foil and bake an additional 15 minutes until the cheese is bubbly and golden brown.
Allow the lasagna to rest for 10 minutes before slicing. This resting time helps the layers set and makes serving easier. Enjoy your fresh and flavorful Summer Squash & Ricotta Pesto Lasagna with a crisp green salad or some garlic bread for a complete meal.