Marinate chicken thighs in yogurt, olive oil, garlic, Dijon mustard, oregano, black pepper, cumin, salt, lemon zest and juice
Cook the marinated chicken until fully cooked
Prepare tzatziki by combining cucumber, Greek yogurt, dill, olive oil, garlic, lemon zest and juice, and salt to taste
Warm the pitas
Slice the cooked chicken
Assemble gyros by filling pitas with sliced chicken, tzatziki sauce, sliced tomato, and fries