In a large bowl, whisk together flour, water, eggs, salt, and oil until completely smooth to make the crepe batter.

Refrigerate the batter for at least 30 minutes to rest.

Heat a 6-inch skillet over medium heat and lightly brush with oil.

Pour about 1/3 cup of batter into the skillet, immediately tilting and rotating to spread it into a thin, even layer.

Cook for about 1 minute until the edges turn golden brown and begin to lift from the pan.

Carefully flip the crepe and cook for an additional 30 seconds until spotted with brown.

Transfer the cooked crepe to a plate and stack with wax paper between each to prevent sticking.

In a separate large bowl, combine ricotta cheese, mozzarella cheese, grated Parmesan, egg, chopped parsley, salt, and pepper to make the filling.

Preheat oven to 350°F. Spread a thin layer of marinara sauce in a 13x9-inch baking dish.

Place about 1/4 cup of the cheese filling down the center of each crepe, then roll it up.

Arrange the rolled manicotti seam side down in the prepared baking dish.

Spoon the remaining marinara sauce over the manicotti and sprinkle with 1/2 cup of grated Parmesan cheese.

Bake for 30-45 minutes, or until the sauce is bubbling and the manicotti are heated through.