Preheat your oven to 350 degrees F. Line an 8x8-inch baking pan with parchment paper, letting the edges hang over for easy removal.

In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Add the whole egg, egg yolk, and vanilla extract, and mix until well combined.

Add the flour, cinnamon, baking powder, and salt. Use a rubber spatula to fold the mixture together until just combined—no streaks of flour should remain.

Fold in the oats, shredded coconut, chocolate chips, and chopped pecans until evenly distributed throughout the batter. Be careful not to overmix.

Transfer the batter to the prepared pan and spread it evenly to the edges.

Bake for 25 to 30 minutes, until the cookie bars are golden brown around the edges and puffed up. The center may still look slightly underdone—it will set as they cool.

Let the bars cool completely in the pan, then lift them out using the parchment paper. Cut into 9 large squares or 16 smaller portions and serve.