In a large bowl, add the drained tuna and gently flake it with a fork. Add the tomato, jalapeño, red onion, and cilantro.
In a small bowl, whisk together the mayo, sour cream, Mexican crema, lime juice, pickled jalapeño brine, salt, and black pepper.
Pour the dressing into the large bowl and toss until everything is well coated. Gently fold in the diced avocados.
Serve immediately with crackers, tortilla chips, tostadas, or lettuce cups.
Notes
Storage. Keep it in an airtight container in the fridge. It's safe for up to 4 days, but it's best within 2 because the tomato releases water and the avocado browns. Press plastic wrap onto the surface before sealing to slow the browning.
Drain the tuna well. Pour it into a sieve and let it sit while you chop the vegetables. If it's wet going in, the salad will be watery.
The tomato seeds and pulp. Scooping them out is what keeps the dressing creamy instead of thin. Roma holds up better here than a beefsteak or vine tomato.
Pickled jalapeño brine. Just the liquid from a jar of pickled jalapeños. Chop up a few of the actual jalapeños and add those too if you want more heat.