Season chicken thigh with salt and pepper. Whisk together garlic, mustard and vinegar in a dish. Add chicken and turn to coat. Cover and then put in fridge for at least half an hour
Preheat a barbecue plate or a George Forman grill on high heat. Remove chicken from marinade. Lightly spray chicken with oil. Cook for 1 minute each side or until golden. Reduce heat to medium-low. Cook chicken until cooked through
Slice chicken. Combine beans, tomato, feta, rocket and chicken in a large bowl. Toss gently. Spoon onto plates. Season with pepper. Serve with a wedge of lemon.