Place
the cream cheese, mozzarella, feta, and chopped baby spinach into a
large mixing bowl. Massage the spinach and the cheeses with your hands
until they are well combined (it should look like a thick paste). Set
aside.
Place the flounder fillets onto a large board. Sprinkle the desired amount of Old Bay Seasoning onto each fillet.
Divide
the stuffing into 6 equal portions. Working one at a time, shape the
portion of the stuffing into an egg shape and place it close to the tail
of the fish. Then starting from the tail, roll each fillet up
jelly-roll style and place it seam side down on the baking dish.
Sprinkle some more Old Bay seasoning on top, and using a pastry brush, spread some olive oil over the fillets.
Bake at 350ºF for about 20 minutes, until the fish is cooked through.
