On a clean work surface, make a mound with the flour and create a well in the center.Crack the eggs into the well, add the olive oil and a pinch of salt.Using a fork, gradually mix the flour into the eggs until a dough begins to form.
Knead the dough for about 10 minutes until smooth and elastic.Wrap the dough in plastic wrap and let it rest for 30 minutes.
In a mixing bowl, combine the ricotta cheese, Parmesan cheese, chopped spinach, egg yolk, salt, pepper, and nutmeg (if using).Mix until well combined and set aside.
Divide the dough into two equal portions.Roll out one portion on a floured surface or use a pasta machine until it's about 1/8 inch thick.Repeat with the second portion of dough.
Place small dollops of the filling (about 1 teaspoon each) on one sheet of dough, spaced about 1 inch apart.Brush around the filling with water to help seal.Place the second sheet of dough over the first and press around the filling to remove air pockets.
Use a ravioli cutter or a knife to cut out individual ravioli. Press edges with a fork if not using a cutter.
Bring a large pot of salted water to a boil.Gently add the ravioli and cook for 3-4 minutes or until they float to the top.Remove with a slotted spoon and drain in a colander.
Warm the marinara sauce in a saucepan over medium heat.Plate the ravioli, top with marinara sauce, garnish with fresh basil, and sprinkle with grated Parmesan cheese.