Preheat the oven to 350 degrees. Butter a 9x9 baking dish and line it with parchment paper, then set aside.
Whisk together oats, brown sugar, baking powder, cinnamon, and salt.
Stir in the chocolate chips and pecans, then set the bowl aside.
In a separate bowl, combine the cooled melted butter and sourdough discard.
Add the eggs and vanilla extract, whisking until fully combined.
Add the oat mixture to the butter mixture, alternating with the milk, and mix until incorporated.
Pour into the prepared dish and spread evenly. Bake for 30-35 minutes, until the edges are golden and the center is set.
Cool completely before slicing.