Whisk together 4 cups of the flour, baking soda, and salt. Set aside.
Using an electric mixer on medium speed, beat the butter, granulated sugar, and brown sugar until light and creamy. Add the eggs and vanilla, mixing well.
Reduce the mixer speed to low. Gradually add the flour mixture, mixing just until combined.
Divide the dough in half. To one half, add the cocoa and mix just until combined. To the other half, add the remaining 1/4 cup flour and mix just until combined.
Stir into each dough 1 cup oats and 1 cup chocolate chips.
Cover and refrigerate for 2 hours.
Preheat oven to 375°F (190°C). Line baking sheets with parchment paper or silicone liners.
Combine 1 tablespoon of each dough, twisting together to make one cookie. Place 2 inches apart on the prepared pans. If the dough becomes too warm, refrigerate for a few minutes then resume forming the cookies.
Bake about 10 minutes or until the lighter dough is golden brown. Cool on the pans for 2 to 3 minutes. Then, remove the cookies to wire racks to cool completely.