Peel the plantains by scoring them horizontally (end to end) with a knife. Turn them to the other side and score it again. Carefully peel the skin off and discard the skin.
Slice the plantains cross-wise into medallions or coins. Transfer to a bowl and toss with the oil until lightly coated.
Spread the plantain medallions in one even layer on a lined baking sheet.
Bake for 15 minutes. Remove from the oven and carefully turn each slice over.
Return the sheet pan to the oven and bake another 10-15 minutes, until golden.
Allow to cool 2-3 minutes, then transfer to a serving bowl or plate.
Notes
* Ripe plantains should be very yellow with lots of dark spots or lines on the peel.