Follow these detailed steps to ensure a perfect avocado tuna salad every time. The key is in the preparation and the gentle mixing to maintain a wonderful texture.

1. Prepare Your Vegetables: Begin by meticulously preparing your produce. Finely dice the red onion and the celery stalks. The smaller the dice, the better the texture of the final salad, ensuring you get a little bit of everything in each bite. Chop your fresh cilantro (or other herb of choice). Set these prepared vegetables aside in a small bowl.
2. Mash the Avocado Base: Slice your avocados in half lengthwise and remove the pits. Scoop the flesh into a medium-sized mixing bowl. Using a fork, mash the avocado against the sides of the bowl until it reaches your desired consistency. Some prefer it completely smooth and creamy, while others like a few small chunks for texture.
3. Add the Flavor Enhancers: Immediately after mashing, add the freshly squeezed lime juice and the Dijon mustard directly to the avocado. Mix them in thoroughly. This step is crucial because the acid from the lime juice begins to work right away to prevent the avocado from turning brown.
4. Incorporate the Tuna: Open your cans of tuna and drain them completely. Press the lid against the tuna to squeeze out as much water as possible. Flake the drained tuna directly into the bowl with the avocado mixture. Use your fork to gently break up any large chunks of tuna.
5. Combine All Ingredients: Add the diced red onion, celery, and chopped cilantro to the bowl. Sprinkle in your initial amount of salt and freshly ground black pepper.
6. Gently Fold and Mix: Using a spatula or a large spoon, gently fold all the ingredients together. Be careful not to overmix! The goal is to combine everything until it’s just incorporated. Overmixing can create a pasty texture; gentle folding preserves the distinct textures of the tuna flakes, crunchy celery, and creamy avocado.
7. Taste and Adjust Seasoning: This is the most important step for a perfect result. Take a small spoonful and taste the salad. Does it need more salt? A bit more of a kick from black pepper? Another squeeze of lime juice for brightness? Adjust the seasonings now until the flavor is perfectly balanced to your liking.
8. Prepare the Lettuce Cups: Carefully peel the leaves from the head of lettuce. For Butter lettuce, the leaves will naturally form perfect little cups. For Iceberg or Romaine, you may need to trim the bottom stem slightly. Rinse the leaves under cool water and pat them completely dry with a paper towel or use a salad spinner. Moisture on the lettuce can make the wraps soggy.
9. Assemble and Serve: Spoon a generous amount of the avocado tuna salad into each lettuce cup. Arrange them on a platter and serve immediately for the best experience, enjoying the contrast between the chilled, creamy salad and the crisp, fresh lettuce.