Heat the oven to 400°F and spread the orzo in a 9-by-13-inch baking dish.
Pour in the broth and lemon juice, then stir in the zest, frozen peas, salt and black pepper.
Arrange the chicken thighs over the orzo and press them down until their bottoms touch the liquid.
Cover tightly with foil and bake for 25 minutes.
Lift the chicken briefly, stir the orzo from the corners, replace the chicken and bake uncovered for 15 to 20 minutes more.
Check that the chicken reaches 165°F and the orzo is tender, then rest the dish for 5 minutes.