Preheat oven to 350 degrees. Use 1/2 tablespoon of softened butter to grease a 9 x 9 baking dish then set aside.
Remove the pit from the peaches, leave the peel on and slice into about 1/2 to 1″ chunks or cubes. Place peaches in a large bowl. Add granulated sugar, cornstarch, lemon juice, cinnamon and vanilla extract. Gently stir until peaches are evenly coated then transfer to the prepared baking dish.
Melt butter, add to a medium to large bowl and blend with oats, flour, brown sugar, cinnamon and salt. Stir until the mixture is crumbly. Use your hands to evenly sprinkle the topping over the peaches.
Bake 30–35 minutes or until the peach juices are bubbling around the edges and the topping is lightly golden brown.
Remove from oven, cool 10-15 minutes. Serve warm to room temperature – plain or with scoops of vanilla ice cream.