Buying ready-picked white crab meat is such a good cheat here, and makes it easy to put these tacos together in minutes. The only cooking you need to do is warming up the tacos! I love the combination of sweet crab with hot, aromatic harissa, but you can use any chilli paste or hot sauce you like to get a kick, or leave it out altogether if you don’t like the heat; the tacos will still be delicious.