Preheat your oven to 180°C (350°F). Grease your baking pan with butter or line it with parchment paper.

In a large bowl, whisk together the oats, baking powder, cinnamon, and salt. Set aside.

In a separate bowl, whisk together the milk, egg, melted butter, brown sugar, and vanilla extract until smooth.

Pour the wet mixture into the dry ingredients and stir until fully combined. The batter will be thick but scoopable.

In a small bowl, combine the brown sugar, cinnamon, and melted butter. Stir until smooth.

Spread half of the oatmeal batter evenly in the prepared pan. Drop spoonfuls of the cinnamon swirl mixture on top and gently swirl with a knife or skewer. Spread the remaining oatmeal batter over the top and lightly swirl again for a marbled effect.

Bake in the preheated oven for 35–40 minutes, or until the top is golden and a toothpick inserted into the center comes out clean.

While the oatmeal is baking, whisk together the cream cheese, powdered sugar, milk, and vanilla extract until smooth.

Once baked, allow the oatmeal squares to cool for 5–10 minutes. Drizzle with the cream cheese glaze. Slice into squares and serve warm.

Optional: Sprinkle with chopped nuts or extra cinnamon sugar for added texture and flavor.