12 ounces boneless skinless chicken breasts, cut into 4-inch-long, 1-inch-thick strips
2 teaspoons Mediterranean Spice
4 romaine lettuce leaves, shredded
1 tablespoon thinly sliced red onion
1/4 cup Tzatziki
12 butter lettuce leaves
4 Roma tomatoes, chopped
1 1/2 ounces crumbled feta cheese
12 kalamata olives, pitted and chopped
1 teaspoon chopped parsley
1/2 teaspoon dried basil
1/2 teaspoon dried oregano
Preheat a grill pan over high heat. Season chicken with 1 teaspoon Mediterranean spice and place on grill. Cook, basting with balsamic vinaigrette and turning once, until cooked through, about 2 minutes per side. Season chicken with remaining teaspoon Mediterranean spice and remove from grill; set aside.
Place shredded romaine lettuce and red onions in a medium bowl; drizzle with red-wine vinaigrette and toss to combine. Divide mixture evenly among butter lettuce leaves and drizzle each with 1 teaspoon tzatziki.
Top each taco with 1 piece of chicken and garnish with chopped tomatoes, feta cheese, and olives. Season with parsley, basil, and oregano; serve.