Bring a medium pot of water to a boil. Set the ricotta in a fine-mesh sieve or colander lined with cheesecloth and let drain while you prepare the spinach. You want to remove as much excess moisture as possible.

Add the spinach to the boiling water and cook until tender and bright green, about 2 minutes. Drain the spinach, squeezing out as much excess moisture as possible, then finely chop.

Transfer the drained ricotta to a large bowl and mix in the chopped spinach, bread crumbs, and Pecorino Romano. Add the egg and salt and pepper to taste, and mix well.

At this point, you should have a dense mixture and should be able to roll it into balls roughly the size of a ping-pong ball, about 1 1/2 inches in diameter. If it is too loose or too wet to roll, add more bread crumbs until the mixture is firm enough.

In a large deep sauté pan, heat the olive oil over medium heat until shimmering. Add the ricotta balls (working in batches, if needed) and fry until golden all over, 3 to 4 minutes. Stir them with a spider strainer while cooking so they brown evenly on all sides.

Serve as is or on a bed of marinara.