Preheat your oven to 375°F (190°C). Prepare a baking dish by spraying it with non-stick cooking spray.
Slice the zucchinis lengthwise into thin strips using a mandoline slicer or a sharp knife. You should aim for about 1/8-inch thick slices.
In a bowl, mix together the ricotta cheese, Parmesan cheese, egg, minced garlic, dried oregano, salt, and pepper until well combined.
Spread a thin layer of marinara sauce on the bottom of the prepared baking dish.
Take each zucchini slice and spread a tablespoon or so of the ricotta mixture evenly along the length of the slice.
Carefully roll up each zucchini slice and place it seam side down in the baking dish on top of the marinara sauce.
Once all the zucchini slices are rolled and placed in the dish, spoon the remaining marinara sauce over the top of the roll-ups.
Cover the baking dish with foil and bake in the preheated oven for about 25-30 minutes, or until the zucchini is tender and the cheese is melted and bubbly.
Remove from the oven and let cool slightly. Garnish with chopped fresh basil leaves if desired before serving.