1. Arrange oven rack to lowest third of oven. Heat oven to 450 degree F. Bring the chicken broth and water to a simmer in a medium saucepan.
2. Toss the zucchini and onion with 1-1/2 teaspoons oil on a jelly-roll pan; spread out to cover pan in one even layer. Bake 6 minutes or until edges are golden, stirring once. Remove from oven; set aside.
3. Meanwhile, rub chicken with garlic and salt on a piece of wax paper. Heat the remaining 1-1/2 teaspoons oil in a 12-inch nonstick skillet over high heat until very hot, about 2 minutes. Add the chicken in a single layer and cook, turning once until well browned. Push chicken to one side of pan, add the orzo, and toast, stirring, until golden, 2 minutes. Add the carrots; reduce heat to medium-high.
4. Add the hot broth mixture, 1 cup at a time, every 2 to 3 minutes, stirring continually, as the pasta mixture absorbs the liquid, for 10 minutes using all but 1/4 cup of the broth. Stir in the roasted zucchini-onion mixture and the cheese. Add the remaining 1/4 cup broth if needed (the risotto will absorb more liquid upon standing). Serve immediately, with a grind of pepper, if desired. Makes 6 servings.