Cut your plantains diagonally into slices about 1/2" thick.
Place the plantain slices in a bowl, add the oil, and toss them gently to coat them.
Arrange the plantain slices on a baking sheet and place on the middle rack of the oven once it's heated.
Cook for 15 minutes then carefully flip the plantains with a pair of tongs.
Cook for an additional 10 minutes, or until you're happy with the level of caramelization on both sides.
For super delicious plantains, turn on the broiler when the plantains have about 5 more minutes of baking left. Keep a careful eye on them and remove them from the oven when the tops are looking nice and caramelized, even if the 5 minutes isn't quite up.