1. Combine the chicken, breadcrumbs, egg white, lemon rind, garlic, mint and tomato paste in a processor until smooth.
2. Wet your hands and shape the mixture into 4 burgers.
3. Cook the burgers in a non-stick pan until well-browned and cooked through.
4. Slice the buns horizontally.
5. Layer the lettuce, burger, sour cream sauce, tomato and onion on the bottom half of the bun.
6. Place the top half of the bun over it. Serve warm.
7. Sour Cream Sauce: Combine all ingredients. Mix well.

Image courtesy: Flickr/creativecommonsdiongillard