Preheat oven to 350°F. Line an 8×8" pan with parchment paper.

Start by making the streusel. In a medium mixing bowl, whisk together the flour, walnuts, sugars, and salt. Add the cold butter. Use your fingertips to pinch the butter into the dough until well distributed and mixture is sand-like. Store in fridge while preparing the cake.

Make the stewed peaches. Whisk together corn starch and cold water until dissolved. Add the sliced peaches, brown sugar, and cinnamon to a medium skillet over medium heat. Cook, stirring gently, for 5 minutes. Re-stir the corn starch slurry so it's all dissolved, then add to the peach mixture and continue cooking for 30-60 seconds, until the juices have thickened. Remove from the heat and stir in the vanilla extract. Transfer to bowl to cool completely (I sped up the process in the freezer, stirring every 10 min).

In a medium mixing bowl, whisk together the flour, baking powder, cinnamon, and salt. Whisk together non-dairy milk and lemon juice in a liquid measuring cup. Set aside.

In a separate larger mixing bowl, use a handheld mixer or stand mixer to beat together the butter and sugars until light and fluffy then mix in the vanilla. With the mixer on low speed, add a third of the milk and a third of the flour to the butter mixture at a time. Mix until all the milk and flour is incorporated and a smooth batter forms (make sure not to overmix or the cake will be too dense). . 

To make the cinnamon filling, in a separate small bowl pinch together the softened butter, flour, sugar and cinnamon until soft crumbs form.

Pour half the cake batter into the prepared baking dish. Sprinkle filling over the top then caramelized peaches, then pour over remaining cake batter. Sprinkle over streusel topping and lightly press so it sticks.

Bake for 50-55 minutes or until top is golden brown and toothpick inserted comes out clean or with a few moist crumbs. Let cool for at least 30 minutes before slicing and serving. Enjoy!