Preheat the oven to 375 degrees F.
For the orzo: In a 9-by-13-inch baking dish, whisk together 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.
Add the chicken breasts, laying them so most of the chicken is submerged. Top with lemon slices.
Bake, uncovered, until the chicken registers an internal temperature of 165 degrees F, 35 to 40 minutes. Let rest for 5 minutes.