An easy way to get cubes of mango from a whole one is to cut the wide flat sides away from the stone with the skin still on. Then slice a grid into the flesh without cutting through the skin. Push the skin side of the mango piece so it turns inside out, and little skyscrapers of mango will pop up, ready for you to easily slice them off. Do this over the couscous so the juice goes in too. It’s an old trick, but it’s a goodie.