1. Preheat oven to 380 degrees Fahrenheit (190 degrees Celsius). Cut the margarine into small pieces and place at the bottom of a 9-inch round baking dish.
2. Add the sugar and mix. Place in oven for four to five minutes, until they are both melted. Remove from oven and stir.
3. Cut the bananas into slices 1/2–3/4 of an inch thick (try to make them uniform size for a nicer presentation). Place them circle-side down all over the “caramel,” covering the whole area. Sprinkle with cinnamon.
4. Shape the puff pastry into a circle (it doesn’t have to be perfect, but try to get even thickness throughout). Place on top of bananas and press dough to sides of dish.
5. Bake uncovered for approximately 25 minutes, or until dough is baked through. Let cool for five minutes, then carefully take a plate, place it against the dough, and flip it over, leaving the bananas on top. Serve warm.