Preheat oven to 400° F. Spread marinara sauce onto a bottom of a medium baking dish and set aside.
Cut-off and discard zucchini ends and then slice each zucchini 1/8" thick lengthwise.
In a medium bowl, combine ricotta, 1 1/4 cups mozzarella, 3/4 cup Parmesan, and salt.
Taste and adjust salt if desired. Stir in the egg well. If you would like to, add a pinch of pepper.
On each slice of zucchini, spoon a thin layer of sauce, top with a thicker layer of the cheese mixture, and sprinkle a little bit of chopped basil.
Roll up and place in the prepared baking dish.
Sprinkle with remaining 1 1/4 cups mozzarella and then 1/4 cup Parmesan.
Cover with foil and bake for about 18-20 minutes or until zucchini is tender and cheese is melted.
If desired, garnish top with halved grape tomatoes, basil leaves, and a drizzle of balsamic vinegar. This casserole can be served by itself or with a side of white rice. Enjoy!