Drain the cans of tuna thoroughly to remove excess liquid.

In a medium bowl, flake the tuna with a fork into bite-sized chunks.

Add the diced red onion, yellow bell pepper, crumbled feta cheese, mayonnaise, Dijon mustard, and lemon juice.

Gently fold the mixture together until the tuna and vegetables are evenly coated with the dressing. Try not to over-mash so the feta stays distinct.

Season with coarse black pepper and a pinch of salt if needed (taste first, as feta is salty).

Serve immediately piled high on crackers, toasted bread, or over a bed of greens.