Place rosemary, garlic and salt in a mortar and pestle and crush well (or combine in a food processor and pulse until roughly chopped). Transfer to a non-metal bowl and add oil, chilli and lemon juice. Mix well.
Add chicken to marinade, cover and chill a minimum of 1 hour or overnight.
Cook on greased rack over hot coals or gas barbecue grill on high, 10-15 minutes, turning once and basting with marinade every so often.
For mint dressing, whisk mustard, lemon juice, olive oil, and mint leaves in small bowl until well combined. Serve drizzled over chicken (and accompanying vegetables, if desired).