It’s That Simple is our series about recipes so easy, you can make them with your eyes closed. Think tiny ingredient lists, laid-back techniques, and results so delicious you’ll text home about them. Two thousand miles from home, I sat at a white-linen-draped table at Contramar , one of the most celebrated restaurants in Mexico City, totally dumbfounded. I had just devoured their iconic tuna tostada: a shatteringly crisp disk, swooshed with chipotle mayo, shingled with ruby tiles of raw tuna, adorned with avocado and fried leeks. I wish I could have packed it in my suitcase like a luxurious little souvenir. Back stateside, I knew I had to fall down the rabbit hole of trying to replicate it. I sketched out an ingredients list, with sushi-grade tuna parked on the top. After seeking out a nearby fishmonger and calculating what this ingredient would cost me (a precious $30 per pound), I was left with a minor headache. Then I remembered canned tuna is permanently stationed in my pantry, and probably yours too.…