In a large mixing bowl or stand mixer with paddle attachment, combine egg, butter, sugars, and vanilla. Beat on medium-high speed until creamed and well combined, about 4 minutes.

Scrape down the sides of the bowl, add oats, flour, cinnamon, baking soda, optional salt, and beat on low speed until just combined, about 1 minute.

Add chocolate chips, raisins or nuts if using, and beat on low speed until just combined, about 30 seconds.

Using a large cookie scoop or your hands, form approximately 12 equal-sized mounds of dough. Flatten slightly, and place a few chocolate chips on top of each mound.

Place mounds on a plate or tray, cover, and refrigerate for at least 2 hours, up to 5 days.

Preheat oven to 350°F. Line baking sheets with silicone mats or spray with cooking spray. Place dough mounds at least 2 inches apart.

Bake for about 11 minutes, or until edges are set and tops are just set. Cookies may be slightly undercooked in the center, but firm up upon cooling.

Cool on baking sheets for about 10 minutes before transferring to a wire rack. Serve and enjoy!