Preheat oven to 200 ° C (approximately 400 ° F).
Take 4 pieces of aluminum foil measuring about 30x20 cm (approximately 12x8 inches) and place on a flat work surface. Cut or break chocolate into 8x1 cm (approximately 3x.5 inch) wide strips. Peel bananas and cut in half lengthwise. Place one half on a sheet of aluminum foil and place 2 strips of chocolate on top. Top with second half of banana and wrap in foil. Place on a baking sheet and bake for about 15 minutes.
Meanwhile, beat heavy cream until stiff with 2 tablespoons of powdered sugar.
Remove bananas from aluminum foil and cut in half crosswise. Add a dollop of cream and a twig of mint to each plate. Dust with remaining powdered sugar and serve..