Lightly grease an 8 1/2" x 4 1/2" loaf pan and line it with a parchment sling. , Tear or cut peeled bananas into large (2") pieces and place in an 8" square pan, a cast iron skillet, or a small rimmed baking sheet. Cover with the brown sugar and place in the oven. , Preheat the oven to 325°F with the bananas inside. Roast the bananas for 20 to 25 minutes total, stirring every 5 to 10 minutes, until the bananas are very soft and the brown sugar is bubbling. , Carefully transfer the hot mixture to a large bowl and mix vigorously with a potato masher; you should have a liquidy mixture with some small lumps of banana remaining. Set aside to cool for 5 minutes., Once slightly cool, add the oil, egg, and vanilla to the bowl with the bananas and whisk for 1 to 2 minutes, until the mixture is fully emulsified., Add the flour, baking powder, baking soda, and salt, and stir with a flexible spatula to thoroughly combine. Transfer the batter to the prepared pan, smooth the top, and sprinkle with turbinado or sparkling sugar., Bake the banana bread for 45 to 50 minutes, until a toothpick or paring knife inserted into the center of the loaf comes out clean; the internal temperature should register at least 205°F when measured with a digital thermometer., Remove the banana bread from the oven and let it cool in the pan on a wire rack for 15 minutes.  Then remove the loaf from the pan, peel away the parchment, and let it cool completely before slicing and serving., Store leftover banana bread, well-wrapped at room temperature, for 4 days. Freeze for longer storage.