Prep the onion and celery
In a large mixing bowl stir together the pesto, lemon juice and zest, salt, black pepper, olive oil and vinegar
Add the onion and toss to coat
Leave for a few minutes
Add in the celery, rocket, tuna, olives, parsley and toss to coat
Enjoy as is or with warm buttered baguette, or toss with pasta, quinoa, couscous or other grains to bulk it up
