Preheat oven to 200C/180C fan forced. Process walnut, basil and lemon rind in a small food processor until finely chopped. Add tomato and water. Process until thick and spreadable.
Cut a horizontal slit in thickest part of each chicken breast to create a pocket, taking care not to cut all the way through. Fill pockets with pesto mixture. Use toothpicks to secure.
Heat a non-stick frying pan over high heat. Spray with oil. Cook chicken for 2 minutes each side or until golden. Transfer to a baking tray. Bake for 12 minutes until cooked through.
Meanwhile, heat oil in a saucepan over medium heat. Stir in the garlic for 30 seconds. Add the beans and stock. Simmer for 2 minutes. Add juice. Coarsely mash. Season.
Remove toothpicks. Slice chicken. Serve with smash and vege. Enjoy!