Tuna, asparagus & white bean salad

INGREDIENTS

• 1 large bunch asparagus
• 2 x 200g cans yellowfin tuna steaks in water, drained
• 2 x 400g cans cannellini beans in water, drained
• 1 red onion , very finely chopped
• 2 tbsp capers
• 1 tbsp olive oil
• 1 tbsp red wine vinegar
• 2 tbsp tarragon , finely chopped