With a sharp knife, cut your ahi into 1/3 inch thick strips. Every piece of fish will be different, but the end game here is 1/3 inch x 1/3 inch cubes or 1/3inch by 1/2 inch strips. You might notice some fibrous white tissue as pointed to with the knife in the photo below, and just like you might cut fat off of chicken or trim a steak, please remove this and make sure it does not get into your ceviche. It will not kill you, but it definitely isn't fun to chew on.

Once diced up, add your Tuna into a bowl along with the olive oil and gently mix to coat. Mince your cilantro and serrano pepper as well and mix in with the Tuna. Cover with saran wrap or tin foil and place in the fridge for at least 1 hour and up to 2. Make sure however, to remix the ingredients together every 20 minutes to stop the Tuna from drying out and to lock in that great flavor. We do this because Tuna <3' fat, and olive oil is a fat. It locks in flavor and keeps the fish from drying out. (LOVE this next photo btw)

While the covered Tuna marinades in the olive oil in the fridge, measure out all the other ingredients you need. Dice, mince, chop- whatever you really want. Just remember that texturally ceviche is best when everything has a little bit of a different shape and size. If everything is just small cubes, its kinda strange and hard to identify flavors.

When the Tuna has been in the fridge for at least an hour, remove it and mix in all the other ingredients. Stir gently, mixing to coat. Serve with tortilla chips or light crackers and if you want, you can cut up actual tortillas and bake them at 400 for 5-10 minutes to make homemade healthy baked tortilla chips. Super simple and very tasty! Enjoy this lovely recipe!