In the bowl of a stand mixer, or in a large bowl while using a handheld electric mixer, cream together the softened butter, brown sugar, and granulated sugar until creamy, about 2 minutes. Add in the eggs, one at a time, beating well after each addition, followed by the molasses and vanilla extract. Add in the flour, baking powder, baking soda, and ground cinnamon until just barely combined. Beat in the whole oats, and hand-stir in the chocolate chunks.

Cover the bowl and refrigerate the dough for at least 30 minutes, up to 1 hour. If you refrigerate the dough longer, bring it back to room temperature (or close to room temperature) before baking as the dough will get quite hard.

Preheat your oven to 350 degrees F. Line 2 baking sheets with parchment paper or silicone liners. Drop heaping & rounded Tablespoonfuls of dough onto the cookie sheet, spacing about 2" apart. Bake for approximately 8-10 minutes, rotating pans halfway through baking time to ensure even baking. Cookies may appear slightly underdone; this is okay as they will continue to set up as they cool on the baking sheets. Cool on the baking sheets for 15 minutes before transferring to a wire rack to cool completely.