Combine the flour, eggs, oil and salt in a food processor and pulse until a dough is formed. You can also stir it together in a bowl or on a clean work surface, if you don't have a food processor.
Knead until the dough is elastic, about 8 minutes. Add flour as needed to keep it from being too sticky. Cover with plastic wrap and rest in the refrigerator for at least 20 minutes. Take the pasta dough from the refrigerator, cut in half. Roll each half into long strips using a pasta roller (up to the #4 setting) or use a rolling pin to roll it very thin.
Dusting your work surface with flour, lay the pasta sheets down, and cut the edges to form a perfect rectangle.
On one pasta sheet, add about 1 tbsp of filling spaced out in a 6x3 pattern, to make 18 ravioli. Place the 2nd sheet of pasta over the top. Pat the pasta down around the filling, so there are no air bubbles. Push together the edges of the pasta with the tips of your fingers to seal it all the way around.
Using a pasta cutter, or sharp knife, cut along the strips to form 18 separate raviolis. Again push the edges of each individual ravioli together with the tips of your fingers to seal them.
Fill a pot with water and add 1 teaspoon of salt to the water. Set it over high heat until it's at a low boil. Drop the ravioli carefully into the water and let them cook at a low boil or just under a boil, for about 3-4 minutes, until they float. Take them out of the water and set them on a rack or paper towel to dry slightly.
Heat the butter in a skillet over medium heat. Add the crushed walnuts. Once the butter begins to sizzle, add the ravioli to the pan. Cook for 2-3 minutes, until the butter has slightly browned. Season to taste with salt and pepper before serving.