Mangos contain a large, flat seed that doesn’t separate readily from the juicy flesh, so the flesh needs to be cut away from the seed. Mango flesh can be slippery, so leaving the skin on until you’ve dealt with the seed will help your grip.
Balance the mango on one of its narrow sides, and then slice off one of the wide sides of the fruit. Try to cut as close to the seed as possible, usually about 3/4-inch from the center. Repeat with the other wide side, and then slice off the remaining narrow pieces of fruit.
To dice the mango, cup one of the unpeeled pieces in your palm and use a paring knife to score the fruit into the size of dice you want. Be careful not to cut through the skin of the fruit (or into your hand).
Use your fingertips to pop the mango inside out, and then use the paring knife to slice the dice away from the skin.