Heat oven to 350°F and line two baking sheets with parchment. Whisk oats, flour, baking soda and salt in a bowl.
Beat butter, peanut butter and both sugars until creamy, about 2 minutes. Beat in egg and vanilla, then mix in the dry ingredients just until combined and fold in chocolate chips.
Divide into 24 equal mounds, about 1 1/2 tablespoons each, spacing twelve on each sheet. Flatten gently to about 1/2 inch thick.
Bake one sheet at a time for 10 to 12 minutes until the edges are set and lightly browned; leave on the sheet for 5 minutes before moving to a rack.
Cool completely, freeze in a single layer until firm, then pack in a freezer container with parchment between layers. Freeze for up to 2 months for best quality.
Thaw a cookie at room temperature for 20 to 30 minutes, or microwave one on a microwave-safe plate for 10 to 15 seconds for a softer center. Let the chocolate cool slightly before eating.