Preheat oven to 350°F. Line sheet pan with parchment paper.
In bowl of stand mixer fitted with paddle attachment, or in large bowl with hand-held mixer, beat butter, brown sugar and sugar until creamy, about 2-3 minutes. Add eggs one at a time, mixing after each. Add vanilla and mix until well combined.
In medium bowl, combine flour, baking soda, salt, cinnamon and oats. Add to butter mixture all at once and mix on low until combined.
Use a medium (1½ tablespoon) or large cookie scoop (3 tablespoon) to portion dough and arrange a few inches apart on sheet pans lined with parchment paper.
Bake until edges just begin to turn golden, about 8-10 minutes for smaller cookies, 10-12 minutes for larger cookies.
Repeat with remaining cookie dough.
Sprinkle baked cookies with coarse salt, if desired. Let cookies cool on the sheet pan for 5 minutes, then transfer to a wire rack to cool completely. Enjoy within a few days!