Preheat the oven to 400 degrees F. Lightly grease a 9x13 casserole dish.
Add the orzo, chickpeas, tomatoes, red onion, garlic, and bell pepper to the dish and stir to combine. Top with chicken.
In a large bowl, whisk the oil, vinegar, dijon mustard, lemon juice and zest, Italian seasoning, and salt. Pour in the chicken broth and stir.
Now pour the liquid mixture over the chicken and orzo. You can add sun-dried tomatoes here if using, or wait to add them toward the end. Stir gently so the orzo is submerged. Cover with foil and transfer to the oven.
Bake for 30 minutes. After 30 minutes, remove the foil. Give the mixture a stir, and place back in the oven for another 10 - 12 minutes or until the liquid is mostly absorbed and the orzo is tender.
Let sit for 5 minutes. Add capers, feta cheese, and parsley (if using). Season with salt to taste.