Preheat the oven to 400 degrees. Peel the batatas/boniatos and cut into 1/2 inch cubes. Mix in a large bowl with olive oil and salt. Spread out on a cookie sheet. (I put down aluminum foil for quick clean up). Bake at 400 degrees for about 30 minutes total, stirring every 10 minutes so they don't stick to the sheet. Remove them once you can easily insert a fork all the way through.