In a large bowl, combine ½ cup vegetable oil, ¾ cup dark brown sugar, ½ cup granulated sugar, ⅓ cup applesauce, and 1 tsp vanilla extract. Beat on low speed with a hand mixer for about 2 minutes, until the mixture is smooth and well emulsified.

Add 2 cups all-purpose flour, 1+½ cups rolled oats, 1 tsp baking soda, and ½ tsp salt. Add ½ tsp cinnamon now if using. Stir with a spatula or wooden spoon until the dry ingredients are fully incorporated and the dough is very thick but still soft.

Fold in 1+½ cups dark chocolate chips until evenly distributed.

Cover the bowl and chill the dough in the refrigerator for at least 30 minutes to help prevent spreading during baking.

About 10–15 minutes before you plan to bake, preheat the oven to 375°F (190°C). Line baking sheets with parchment paper and position a rack in the center of the oven.

Using a 2-tablespoon scoop or spoon, portion dough and roll into balls. Place the balls 2–3 inches apart on the prepared baking sheet.

For pillowy, soft cookies: leave the dough balls unflattened. For thinner, chewier cookies: gently flatten each ball to at most 1 inch thick with a small glass or your fingers.

Bake for 8–12 minutes, until the cookies are just barely golden brown around the edges. Oven times vary; check at 8 minutes and add time as needed.

Remove the baking sheet from the oven and let the cookies cool on the baking sheet for at least 10 minutes before transferring them to a cooling rack. The cookies will puff in the oven and settle slightly as they cool.