Place the chicken and lemon in a small frying pan. Cover with water and place over medium heat. Bring to a simmer. Reduce heat to low and simmer for 5 minutes. Remove from the heat and stand covered for 5 minutes or until chicken is cooked through. Remove chicken from poaching liquid and shred with a knife.
Meanwhile, place the lentils in a heatproof bowl. Cover with boiling water. Stand for 2 minutes. Drain. Place in a large bowl.
Add the chicken, capsicum, celery, kale, semi-dried tomatoes and onion and toss to combine. Whisk the vinegar, oil and mustard in a small bowl until combined.
Add dressing to salad and toss gently to combine. Serve the salad sprinkled with the peanuts.