In a medium bowl, combine the diced tuna and fresh lime juice. Ensure the tuna is completely coated. Cover and refrigerate for about 15-20 minutes, allowing the acid in the lime juice to 'cook' the tuna.

After marinating, add the finely chopped red onion, minced jalapeño, diced cherry tomatoes, and chopped cilantro to the bowl with the tuna. Gently mix to combine all the ingredients.

Season the mixture with salt and pepper to taste. Add the diced avocado and fold gently to avoid mashing the avocado.

While the ceviche mixture is resting, heat the corn tortillas in a dry skillet over medium heat for about 30 seconds on each side, or until warmed and slightly toasted.

To assemble the tacos, place a generous spoonful of the tuna ceviche mixture onto each tortilla.

Serve immediately with lime wedges on the side for squeezing over the tacos.