For the plantains: Cut off ends and peel plantain. Slice lengthwise at 1/4-inch intervals. Pan fry lightly on both sides then drain on paper towels. While warm, curve one end to the other and pinch to form circles.
For the filling: Preheat the oven to 350 degrees F.
Heat the oil in a large saute pan, and saute lobster, sofrito, and tomato. Add the tomato juice and let simmer for 10 minutes. Finish with cilantro, salt and pepper. Add bread crumbs and stir until mixture is thick enough to spoon into the plantain "shells". Chill the mixture over an ice bath.
To finish the pionono, fill round plantain "shells" with lobster mixture. Preheat 1/4-inch of vegetable oil in a saute pan. Dredge piononos through flour then beaten egg. Pan fry until brown on 1 side, then turn over and finish cooking in the oven for 10 minutes.