Preheat oven to 375°F (190°C).
In a large bowl, beat butter until creamy. Add brown sugar, white sugar, baking powder, baking soda, cinnamon, and salt. Mix until fluffy.
Add eggs and vanilla extract. Beat until light and fully combined.
Mix in flour just until combined. Stir in rolled oats.
Chill dough for 30 minutes.
Divide dough in half and gently fold frozen blueberries into each half.
Scoop dough into 2-tablespoon balls and place 2 inches apart on an ungreased baking sheet.
Bake Chewy Blueberry Oatmeal Cookies for about 15 minutes until tops are lightly golden and centers are set.
Cool on the baking sheet 10–15 minutes before transferring to a wire rack.