Preheat oven to 400F. Brush large rimmed baking sheet with 2 tablespoons oil. Combine remaining 4 tablespoons oil, garlic, and 1½ teaspoons oregano in bowl. Add potatoes and toss to coat. Sprinkle potatoes with salt and pepper. Sprinkle chicken with remaining 1½ teaspoons oregano, then salt and pepper. Arrange chicken, skin side up, in single layer in center of prepared baking sheet. Arrange potatoes around chicken. Drizzle chicken with lemon juice and any remaining oil mixture from bowl of potatoes.

Roast chicken and potatoes until chicken is cooked through and potatoes are tender, about 1 hour 10 minutes.