Combine lemon juice and olive oil in a bowl. Add the tuna, capsicum, celery and some seasoning and combine.
Arrange lettuce leaves on a plate and the tuna mixture on top. Mix mayonnaise and capers together in a small cup and drizzle over the tuna. Finish with olive oil, salt and pepper.
Recipe by The Paleo Network at https://paleo.com.au/recipe-tuna-celery-salad-tartar-dressing/