For the pancakes:
1 cup all-purpose flour
2 teaspoons baking powder
1/2 teaspoon salt
1 cup milk
1 large egg
1 tablespoon vegetable oil
For the cinnamon filling:
1/2 stick unsalted butter, room temperature
1/4 cup plus 2 tablespoons brown sugar
1 1/2 teaspoons ground cinnamon
Make the cinnamon filling: In a medium bowl, stir together the butter, brown sugar, and cinnamon. Scoop the filling into a quart-sized heavy zip baggie, and set it aside.
Make the pancakes: In a medium bowl, whisk together the flour, baking powder, and salt. Whisk in the milk, egg, and oil, just until the batter is moistened.
Heat a large, nonstick skillet over medium heat, and spray it with nonstick spray. Use an ice cream scoop to add the batter to the pan. Use the bottom of the scoop or cup to spread the batter into a circle, about 4 inches in diameter. Reduce the heat to medium low. Snip the corner of your baggie of cinnamon filling, and squeeze the filling into the open corner. When your pancake begins to form bubbles, add the filling. Starting at the center of the pancake, squeeze the filling on top of the pancake batter in a swirl, just as you see in a regular cinnamon roll. Cook the pancake 2 to 3 minutes, or until the bubbles begin popping on top of the pancake and it's golden brown on the bottom. Slide a thin, wide metal spatula underneath the pancake, and gently but quickly flip it over. Cook an additional 2 to 3 minutes, until the other side is golden as well. When you flip the pancake onto a plate, you will see that the cinnamon filling has created a crater-swirl of cinnamon. Wipe out the pan with a paper towel, and repeat with the remaining pancake batter and cinnamon filling. Rewarm the glaze briefly, if needed. Serve pancakes topped with a drizzle of glaze.