Peel plantain and boil in salted water for about 12 minutes. You want the plantain to be cooked through, but not overly soft.
Drain plantain and let it cool. Once plantain has cooled, use a potato ricer or a fork to mash the plantains. Make sure no clumps remain.
Add flour and salt, then use a fork to make a well in the middle and pour in egg and olive oil. Beat the egg, then use your fork to slowly incorporate the flour, egg, and the mashed plantain. Once everything is incorporated, begin to kneed the dough. Be careful not to over knead. The dough will be sticky, but should form a ball. Add more flour as needed.
Let dough rest in the fridge for 20 minutes. Then roll the dough into a log and cut into 6 equal pieces. Roll each piece into a log again, then cut off small squares. Hold each square in the palm of your hand and slowly roll the back of a fork across the surface of the gnocchi to shape the dumplings and create small wedges. The ridges will help the sauce stick to the pasta.
Bring 4 cups of water to a boil. Add salt, then slowly add the gnocchi one by one. The gnocchi will be done when they rise to the top, approximately 1 minute. Use a strainer to remove the gnocchi from the pot.
Assemble the dish by plating a spoonful of gnocchi onto a plate. Laddle some of the ragu sauce on top of the gnocchi, then add pieces of the oxtails. Top with fresh flat leaf parsley and shredded Parmesan cheese (optional).