1. In a medium bowl, mix together sunflower oil, lemongrass, lime, brown sugar, garlic, fish sauce and honey. Place lamb in bowl and rub all over well with marinade and let marinade for 20 minutes.
2. In the meantime, to make pineapple salsa, toss all ingredients in a medium bowl. Cover and place in refrigerator until ready to serve.
3. Heat grill to medium-high heat. Grill on each side for 2-3 minutes to form grill marks. Reduce heat to medium and cook for 10-12 minutes on each side for Medium-rare or leave longer until desired doneness.
4. Remove from from grill and tent with aluminum foil to rest for for 10 minutes.
5. Grill tortillas for 1-2 minutes on each side. Wrap in tea towel to keep warm.
6. Thinly slice lamb and divide on tortillas, top with pineapple salsa and fresh mint. Serve with extra salsa and lime.