In a non-stick frying pan over low heat, heat 1/4 cup oil. Add leek and sauté until soft and caramelized. Add garlic, spinach, and salt, and stir to cook through.

Transfer mixture to a tall, deep container and add nuts and water. Blend with immersion blender until smooth. In a bowl, combine pesto with chicken, stir to coat, and allow to marinate for 20 minutes.

In a frying pan, heat a little oil. Add chicken and fry until cooked through, turning once in middle. Repeat with remaining chicken and serve immediately.