Prep the lettuce. Gently separate the leaves and rinse them.
Pat dry with a clean towel or spin in a salad spinner. Dry leaves = better crunch and no sogginess.
Drain the tuna. Press the lid into the can to remove extra liquid. The drier the tuna, the better it will absorb your dressing.
Make the dressing. In a medium bowl, whisk together mayonnaise (or Greek yogurt), Dijon, lemon juice, a drizzle of olive oil if using, a pinch of salt, and a few grinds of black pepper. Taste and adjust acidity or salt.
Fold in the mix-ins. Add the tuna, celery, cucumber, red onion, and herbs.
Use a fork to gently combine, breaking up big chunks without turning it pasty. If it looks dry, add another teaspoon of mayo or a splash of lemon.
Taste and tweak. Add more lemon for brightness, more pepper for bite, or a pinch of salt to sharpen flavors. For heat, stir in red pepper flakes or a dash of hot sauce.
Assemble the wraps. Lay out 2–3 lettuce leaves per wrap for sturdiness.
Spoon on a generous mound of tuna mixture. Add avocado slices and cherry tomatoes if using.
Wrap and serve. Fold the sides inward and roll like a mini burrito, or leave them open-taco style. Serve immediately while the leaves are crisp.