Steps
1. Make sauce with onions, tomatoes, vinegar, salt and seasonings in a large skillet over medium heat; when begins to boil lower heat.
2. Prepare mashed bananas with margarine and add to the sauce and put it in a baking pan in oven for 15 mn at 375 degrees F.
3. Serve immediately, because bananas tend to harden when cooled.

Source
Compa?ia Bananera de Costa Rica, STARGARDTER, F. (ED), All you need is under the peel - green bananas recipes, Golfito