1. Cut the salmon into large chunks. Drain and rinse the beans. Add salmon, beans, half the baby spinach, mustard, 1 tbsp olive oil, salt (in moderation) and pepper to the food processor and grind finely. Using wet hands, shape the mixture into 4 burgers.
2. Heat 1 tbsp olive oil in a frying pan and fry the salmon burgers 10 minutes on medium heat, or until golden brown, turning halfway.
3. While burgers cook, clean the food processor. Add 1 cup spinach, feta cheese, capers and remaining oil to the food processor and pulse to make a pesto. Add more olive oil if necessary. Season with pepper.
4. Pit and slice the avocado. Split the buns and spread the bottom halves with the spinach pesto. Top with remaining spinach, salmon burgers and avocado. Top with remaining bun halves. Serve, passing the extra pesto separately.
Per serving: 451 calories, 23g fat, 6g saturated fat, 17mg cholesterol, 679mg sodium, 50g carbohydrate, 12g fiber, 5g sugar, 16g protein