Add the olive oil, lime juice, shallot, and some of the parsley to the bottom of a small mixing bowl.
Stir the dressing and set aside.
Drain the tuna very well and add it to the bowl.
Prepare your avocado (dice or mash it) and add it to the bowl.
Add the remaining parsley and gently stir to combine.
Taste and adjust the salt and pepper.
Serve immediately and enjoy!