Prep. Preheat your oven 350°F. Prepare your baking sheets for nonstick.
Dry Ingredients. In a medium mixing bowl, use a whisk to combine together the flour, baking powder, baking soda, cinnamon, and (optional) salt.
Cream. Next, in a mixing bowl, beat together the softened butter, brown sugar, and granulated sugar until creamy, light and fluffy.
Egg. Add the egg, along with the vanilla extract, to the mixing bowl and mix until combined.
Combine. Add the dry ingredients from the first bowl to the mixing bowl and mix until just combined, taking care to not over-mix.
Oats. Use a rubber spatula or similar item to fold in the remaining ingredients (oats, chips, and nuts).
Scoop. Use a small cookie scoop to scoop out the cookie dough and place it onto the prepared baking sheets, leaving space between the cookies for spread.
Bake. Bake the cookies for 12-15 minutes, or until the edges of the cookies are golden brown.
Cool. Let the cookies sit on the sheets for a few minutes before transferring them to a cooling rack to fully cool.