Shred 1/4 of the English cucumber. Add it to a small bowl with the Greek yogurt, garlic powder, dill, lemon juice, salt, and pepper.
Season the chicken breasts with the Greek seasoning. Spray a nonstick pan with cooking spray and cook the chicken breast 3-4 minutes on each side over medium heat, or until it reaches an internal temperature of 165 degrees.
Assemble the bowls by adding the rice, chicken, tomatoes, chickpeas, feta cheese, red onion, cucumbers, and tzatziki sauce.