Preparation Put oven rack in middle position and preheat oven to 375°F. Butter a large baking sheet. Stir together oats, flour, baking soda, and salt in a bowl to combine. Whisk together brown sugar, butter, egg, vanilla, and zest in another bowl. Stir egg mixture into flour mixture until just combined. Stir in chocolate chips. Make 12 mounds of batter 1 1/2 inches apart on baking sheet. Bake until cookies are golden and edges are crisp, about 15 minutes. Transfer cookies to a rack to cool.
Preparation Put oven rack in middle position and preheat oven to 375°F. Butter a large baking sheet. Stir together oats, flour, baking soda, and salt in a bowl to combine. Whisk together brown sugar, butter, egg, vanilla, and zest in another bowl. Stir egg mixture into flour mixture until just combined. Stir in chocolate chips. Make 12 mounds of batter 1 1/2 inches apart on baking sheet. Bake until cookies are golden and edges are crisp, about 15 minutes. Transfer cookies to a rack to cool.