Heat oil in a deep skillet or pot over medium heat until it reaches a shallow frying temperature (about 325–350°F), or until oil shimmers.
Pour the buttermilk into a bowl. Place the flour in a separate bowl or large resealable bag, and the bread crumbs in a third bowl or bag.
Working in batches, dip about 10 ravioli into the buttermilk, turning to coat both sides thoroughly.
Transfer the wet ravioli to the flour and toss or shake to coat evenly, then return them briefly to the buttermilk to re-wet all sides.
Move the ravioli to the bread crumbs and press or shake so each piece is fully coated in crumbs.
Carefully add coated ravioli to the hot oil and fry until golden brown, about 1–2 minutes per side depending on oil temperature and ravioli thickness.
Remove fried ravioli with tongs or a slotted spoon and drain on paper towels; sprinkle with the grated Parmesan while still hot.
Repeat the breading and frying process with remaining ravioli, then serve immediately with marinara for dipping.