Heat olive oil in a skillet. Saute onion and jalapeno, stirring constantly.
Add the diced tomato to the skillet. This will only take 3-4 minutes.
Drain the canned tuna and add it to the skillet. Cooking this dish will only take 5 minutes from here.
Season with salt. Mix all the ingredients to combine. You can also add a pinch of oregano and a squeeze of lime juice for some added flavor.
Serve with saltine crackers, on a homemade tostada, or with a handful of chips. Atún a la Mexicana is a tasty blend of spicy and delicious.