open faced healthy tuna melt

Ingredients

• 1 can flaked white tuna, drained
• 1 - red onion, finely chopped
• 1/4 cup black olives, chopped
• 1/2 - tomato, chopped
• 2 tablespoons parsley
• 1/2 cup olive oil
• 2 tablespoons red wine vinegar
• - pita bread rounds
• 1/2 cup feta cheese crumbles