Preheat oven to 375°F. Gather all ingredients.
Whisk together cinnamon, ¾ cup of the flour, ¼ cup of the brown sugar, and ¼ teaspoon of the salt in a medium bowl. Using a fork, stir in ¼ cup of the melted butter until large clumps form and no dry flour remains; refrigerate, uncovered, until ready to use.
Whisk together baking powder, ¾ cup of the brown sugar, and remaining 1 ¼ cups flour and ½ teaspoon salt in a medium bowl; add milk and maple syrup, stirring until just combined. Pour remaining ½ cup melted butter into a 13- x 9-inch baking dish in an even layer. Pour batter evenly over butter in dish (do not stir); set aside.
Bring peaches, lemon juice, and remaining ½ cup brown sugar to a boil in a large saucepan over high, stirring occasionally. Remove from heat; spoon peaches and any juices evenly over batter in prepared dish (do not stir).
Bake in preheated oven for 20 minutes. Sprinkle evenly with chilled streusel mixture. Bake at 375°F until golden brown, about 20 minutes. Let cool slightly for 5 minutes. Serve warm with vanilla ice cream.
