In a large bowl, combine the sliced peaches, lemon juice, vanilla extract, 2 tbsp flour, ¼ cup granulated sugar, ½ tsp cinnamon, and a pinch of salt. Preheat the oven to 375 F.
Place the peaches and juices in a greased 9x13-inch casserole dish.
Make the topping: combine ¾ cup flour, rolled oats, ½ cup granulated sugar, ¼ cup brown sugar, 1 tsp cinnamon, ¼ tsp nutmeg, and ¼ tsp salt in a medium-sized bowl.
Cut in the diced butter using two knives, a pastry blender, or your hands, until it resembles coarse sand and sprinkle this topping evenly over the peaches.
Bake for 30-40 mins or until golden brown. Let it rest for 10 minutes before serving.