Creating the Sheet Pan Chicken Shawarma Havarti Sandwich is a breeze when you follow these steps:

1. Preheat the oven: Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
2. Prepare the chicken: In a large mixing bowl, combine olive oil, shawarma spice blend, salt, and pepper. Add the chicken thighs, ensuring they are well coated with the marinade.
3. Arrange on the sheet pan: Place the seasoned chicken thighs on the prepared baking sheet, spreading them out evenly.
4. Roast the chicken: Roast the chicken in the preheated oven for 25-30 minutes, until cooked through and slightly charred on the edges.
5. Rest the chicken: Remove the pan from the oven and allow the chicken to rest for about 5-10 minutes before slicing.
6. Prepare the bread: While the chicken is resting, warm the pita breads or sandwich rolls in the oven for 5 minutes.
7. Slice the chicken: Once rested, slice the chicken thighs into strips or bite-sized pieces.
8. Assemble the sandwich: On each warmed pita or roll, layer sliced chicken, Havarti cheese, shredded lettuce, tomato slices, cucumber, and red onion.
9. Add dressing: Drizzle your choice of dressing over the top and sprinkle with fresh parsley, if desired.
10. Serve: Immediately serve the sandwiches while the chicken and cheese are warm and enjoy!