Preheat the oven to 350°F. Cut plantains into very thin slices (about 1/8-inch thick), either with a knife or on a mandoline or Japanese benriner. Place slices into a bowl and toss with oil. Sprinkle Ranch seasoning over the plantains and shake to coat evenly. Spread in an even layer on a lightly greased sheet pan. Bake for about 25 minutes, flipping once halfway through, until golden brown and crisp.
For safe meat preparation, reference the USDA website.