Preheat the oven to 375 degrees F.
To prepare the patty pan squash, cut a small slice off the bottom of each squash so that it sits flat. Remove the top of the squash and use a melon-baller or small spoon to scoop out the interior flesh of the squash. Make sure to not puncture through the sides or bottom of the patty pan squash. Repeat for all the squash and set aside.
Next make the ricotta filling. Add the ricotta, Parmesan, lemon zest, basil leaves, salt and pepper to a mixing bowl and mix to combine.
Add 1-2 tablespoons of the ricotta filling into each of the hollowed out patty pan squash. Set aside for now.
In a large 9x12 inch baking dish, add 2 cups of tomato sauce to the bottom of the dish, spreading it out into an even layer. Add the stuffed patty pan squash to the baking dish, evenly spacing them out. Add the remaining tomato sauce so that it comes 1/3 of the way up the patty pan squash.
Cover the baking dish with aluminum foil and bake in the centre of the oven for 45 minutes. The patty pan squash will be done when you can insert a fork into the squash and it goes in smoothly.
To serve, place the squash on a plate with some tomato sauce. Garnish with fresh basil leaves and a drizzle of olive oil. Enjoy!