• In a small saucepan, bring beef stock to a simmer over medium heat. Add butter and couscous, stirring to combine. Cover pan, and remove from heat. Let stand for 10 minutes.
• Fluff couscous with a fork, and transfer to a medium bowl. Add tomato, cucumber, 2 tablespoons mint, feta, pine nuts, lemon zest, lemon juice, ¾ teaspoon salt, and ½ teaspoon pepper. Set aside.
• Place a lamb slice between 2 sheets of plastic wrap, and pound gently, using the flat side of a meat mallet, until twice as thin and almost doubled in size when flat. Repeat with remaining lamb slices. Set aside.
• Remove thick center ribs from grape leaves. Lay leaves flat on a work surface. Place 2 to 3 tablespoons couscous filling on the bottom part of the grape leaf. Roll up, tucking in the edges, until a firm, cylindrical shape is created. Repeat with remaining couscous and grape leaves.*
• In a small bowl, combine ¾ teaspoon cumin, 3 tablespoons avocado oil, ¾ teaspoon salt, and ½ teaspoon pepper to taste. Brush both sides of 1 lamb slice with oil mixture.
• Place the rolled grape leaf at the bottom edge of a piece of lamb, and roll together. Skewer the roll with 2 picks, one at either end and one in the middle. Repeat with remaining lamb and grape leaves.
• Heat a grill pan over high heat, and brush with oil. Place dolmades on the grill, and cook, turning once, until browned and grill marks are visible, 3 to 4 minutes per side.
• Meanwhile, in a small bowl, combine yogurt, tahini, remaining 3 tablespoons avocado oil, remaining 3 tablespoons mint, remaining 1 teaspoon cumin, remaining ¾ teaspoon salt, and remaining ½ teaspoon pepper. Place in an airtight container, and refrigerate until ready to use.
• To serve, cut warm dolmades in thirds.
• Garnish yogurt sauce with avocado oil, if desired.

 
*The dolmades can be made up to this point and kept, tightly covered, in the refrigerator for up to 1 day.