Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Zest and quarter lemon. Mince or grate garlic. Pat chicken dry with paper towels. In a medium bowl, combine a drizzle of olive oil, juice from 2 lemon wedges (4 wedges for 4 servings), half the Tunisian Spice, salt, pepper, and garlic (to taste). Add chicken; turn to coat. Set aside to marinate.

Meanwhile, pick dill fronds from stems; discard stems. Chop fronds. Trim, peel, and quarter cucumber. Grate one quarter on the largest holes of a box grater (grate two quarters for 4 servings). Squeeze out excess moisture, then add to a small bowl along with yogurt, 1 tsp dill (2 tsp for 4), salt, pepper, and garlic (to taste). Stir to combine.

Bring 3/4 cup water (11/2 cups for 4 servings) to a boil in a medium pot. Once boiling, add couscous. Lower heat to medium. Simmer until water has absorbed, 6-8 minutes. Turn off heat; stir in a drizzle of olive oil, salt, pepper, and lemon zest (to taste). Meanwhile, dice tomato and remaining cucumber. In a second medium bowl, combine tomato, cucumber, remaining dill, a large drizzle of olive oil, juice from remaining lemon wedges, salt, and pepper.

Microwave 1 TBSP butter (2 TBSP for 4 servings) and remaining garlic in a small, microwave-safe bowl until melted, about 30 seconds. Season with salt and pepper. Cut pitas into 8 triangles (16 triangles for 4). Brush with garlic butter and place on one side of a baking sheet. (For 4, spread across whole baking sheet.)

Heat a large drizzle of olive oil in a large, preferably nonstick, pan over medium-high heat. Add chicken and sear until browned but not yet cooked through, about 2 minutes per side. Turn off heat; transfer chicken to other side of baking sheet. (For 4 servings, transfer to a second baking sheet; bake chicken on middle rack and pita on top rack.) Bake until chicken is cooked through and pitas are lightly toasted, 5-7 minutes. Wash out pan used for chicken.

Pat cheese dry with paper towels. Slice into 4 pieces (8 pieces for 4 servings). Season all over with remaining Tunisian Spice. Heat a large drizzle of olive oil in same pan over medium-high heat. Add cheese and cook until browned and warmed through, 1-2 minutes per side. Thinly slice chicken crosswise. Divide between plates along with cheese, couscous, salad, pita, and tzatziki.