So Easy Salmon Burger

• 250 g salmon fillets, skin off
• .25 red onion, diced
• 2 tsp dijon mustard
• 1 tbsp lemon juice
• .6 cup wholemeal bread crumbs
• 2 tbsp tartare sauce
• 60 g rocket
• 1 Lebanese cucumber, sliced
• 1 tomato, sliced
• 2 grain bread rolls