Heat oven to 425. In a large roasting pan toss potatoes and garlic with 1 1/2 tablespoons oil and 1/2 teaspoon salt. Put the pan in the upper third of the oven and cook, stirring once, for 15 minutes.
Coat chicken with 1 tablespoon of oil; arrange chicken skin side up, in a smaller roasting pan. Sprinkle with lemon juice, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Top each breast with a piece of butter.
Stir potatoes. Put chicken in the oven and cook for 10 minutes. Add the asparagus, remaining tablespoon oil, and 1/8 teaspoon each salt and pepper to the potatoes. Stir and continue cooking until chicken, potatoes, and asparagus are done, 10 to 15 minutes longer. Remove both pans from oven. Toss vegetables with lemon zest and serve with chicken.