To make this Peach Cobbler Coffee Cake Recipe gluten free, substitute the all-purpose flour in both the cake and streusel topping with a high-quality 1:1 gluten-free baking flour blend that contains xanthan gum. In addition, use certified gluten-free old-fashioned oats, as standard oats may be cross-contaminated with wheat during processing. Check that your baking powder, baking soda, and vanilla extract are labeled gluten free as well. The texture may be slightly more delicate than the original version, so allow the cake to cool a bit longer before slicing to help it set properly.