1. Preheat oven to 425° with rack in bottom third. Line the bottom of a (15 1/2- x 12-inch) roasting pan with foil.
2. Combine first 4 ingredients (through pepper) in a small bowl and mash into a paste. Transfer 1 tablespoon garlic-rosemary mixture to another bowl and stir in 1 1/2 tablespoons oil. Add potatoes to roasting pan with oil mixture and toss well. Arrange in a slightly overlapping layer in pan.
3. Add paprika and remaining 1/2 tablespoon oil to remaining garlic mixture. On a work surface with breast side of chicken up, tuck wings underneath. Loosen skin from top of breast and from thigh and leg. Work half of garlic mixture under skin, then rub remaining mixture over chicken. Place lemon inside cavity. Place chicken breast side up on top of potatoes.
4. Roast until a meat thermometer inserted into fleshy part of thigh registers 170°, 1 hour to 1 hour 10 minutes. Transfer to a cutting board and let stand 10 minutes before carving. Serve chicken with pan juices and potatoes alongside.
Latin-style chicken: Leave the rosemary and paprika out of the rub and swap in 1 1/2 teaspoons each dried oregano and ground cumin. Use a quartered orange instead of the lemon in the cavity; serve with wedges of fresh lime.
Asian-style: Skip the olive oil, rosemary, paprika, and lemon. Instead, combine 2 tablespoons finely chopped fresh ginger with garlic and 1 1/2 tablespoons vegetable oil. Place a quartered orange in the cavity in place of the lemon. Melt together 1/3 cup apricot preserves with 2 tablespoons soy sauce and brush over chicken 20 minutes before roasting ends. Serve with brown rice in place of potatoes.