For the orzo: Whisk together the stock, butter, salt, cornstarch, dill, lemon zest and juice and garlic in a bowl. Mix in the orzo.
For the chicken: In a separate bowl, mix together the coriander, salt and pepper. Coat the chicken all over with the seasoning.
Pour the stock/orzo mixture into a glass 9-by-13-inch baking dish. Add the chicken breasts, laying them at an angle so all but the tops of the breasts are submerged. Shingle the lemon slices in between the chicken breasts.
Bake, uncovered, until the chicken registers an internal temperature of 165 degrees F, 35 to 40 minutes. Let rest for 5 minutes. Top with the chopped parsley before serving.