Preheat oven to 350 degrees F. Lightly spray an 8×8 glass baking pan with cooking spray and set aside. Or, you can line the pan with parchment paper, creating an overhand to lift the brownies out of the pan after cooking.
In a medium bowl, whisk together the flour, baking powder and salt together.
Place the oat beverage in a small saucepan and warm over medium-low heat. Add 1/4 cup chocolate chips and cover with a lid, then remove from heat. Let sit for 5 minutes, then stir together so the chocolate melts.
Pour the melted chocolate and oat beverage into a separate large bowl, whisking in the unsweetened cocoa powder, espresso powder, sugar, oil and vanilla extract until the espresso powder and sugar is dissolved.
Add the flour mixture to the chocolate bowl and stir together until just combined. Fold in the remaining 1/4 cup chocolate chips.
Place the batter into the prepared pan and cook for ~30 minutes, or until toothpick inserted into the center comes out mostly clean. Remove pan and let cool for at least 2 hours. Slice into 8 pieces and enjoy!