On a medium-sized frying pan, pour in about a tablespoon of olive oil.
Heat the pan on medium-high heat.
Once the oil is heated, put in the corn tortilla and spice to taste.
Let each corn tortilla sit in the oil for about 2 minutes on each side. It might be longer or shorter depending on how crispy you like your tostadas.
When opening both tuna packages, make sure to drain any excess juices they might have.
In a medium-sized cooking bowl, mix the diced avocados and tuna until combined.
If you want the tuna to be cooked and not raw, then I would recommend cooking it in a pan with about a tablespoon of olive oil and spices of your choice (to taste). You can do this for around 4-5 minutes on high heat, stirring occasionally.
Squeeze some lime on top and mix (optional).
Put two tostadas on a large plate and top them with the tuna and avocado mixture.
Lastly, top with a salsa of your choice and queso fresco (or other cheese of your choice).
Eat them and if you're cooking for one, then eat the other 2 if you're not concerned about calories. They're that good. :)