Preheat grill to 400 F.
In a small bowl mix greek yogurt with harissa paste, season with salt and pepper.
Add chicken thighs to the medium bowl, season with salt and pepper, toss it. Add half the harissa sauce, toss it. Leave remaining harissa sauce for serving.
In a small bowl stir 1 tablespoon of oil, minced garlic and 1 teaspoon parsley. Season with salt and pepper. Brush pita with garlic oil, set aside.
Grill the chicken until cooked for 6-8 minutes on each side. Slice the chicken.
When chicken is almost done, add pita to the grill, cook for 1-2 minutes on each side.
In a large bowl whisk together white wine vinegar with sugar and 1 tablespoon of oil. Add spring mix, cucumber and tomatoes. Season with salt and pepper, toss it.
Spread some harissa sauce on pita bread, add sliced chicken, top it with spring mix. Sprinkle with remaining parsley.