Cut the ends off each plantain, then carefully cut a slit lengthwise down the peel without cutting into the flesh. Use your hands to separate the peel from the fruit. Cut each plantain crosswise into 1-inch rounds.
Add enough oil to just skim coat the bottom of a heavy skillet and set the pan over medium to medium-low heat. Once the oil is hot, add the plantains in a single layer and cook for 2 to 3 minutes on each side, or until lightly golden.
Remove plantains from pan and transfer to a work surface or cutting board. Use a plantain press or the bottom of a drinking glass to press the plantain into rounds about ½-inch thick.
Return plantains to skillet, adding oil if necessary, and cook on each side for 2 to 3 minutes more or until golden brown and crispy. Remove from the pan and transfer to a plate lined with a paper towel. While still hot, sprinkle with sea salt.