In a bowl combine mint and garlic for your marinade. Add lamb shoulder and mix, pressing in the leaves and garlic into the lamb. You can set aside overnight in an airtight container.
For tzatziki, combine cucumber, yogurt and dill in a bowl and add salt and lemon juice to taste. Set aside (you can also make this a day ahead and place in an airtight container).
Place lamb on a hot grill for 10-15 minutes each side or until done. Slice and set-aside. Cut your pita rounds into quarter points and fill with sliced lamb and tzatziki. Garnish with parsley and serve.