Do not drain the zucchini: The moisture from the shredded zucchini helps keep the brownies soft and fudgy.
Let the chocolate mixture cool slightly: Give the melted butter and chocolate a few minutes to cool before whisking in the eggs so they do not scramble.
Stir just until combined: Once the oat flour and cocoa powder are added, mix only until the batter comes together.
Use certified gluten-free oat flour if needed: Oats can be cross-contaminated with wheat, so certified gluten-free oat flour is best for a fully gluten-free brownie.
Cool completely before slicing: The brownies need time to set after baking so they hold together and slice cleanly.