Peel and slice peaches and place in an 8-inch square baking pan. Toss with lemon juice, sugar and cornstarch.
In large bowl, mix flour oats, cinnamon and brown sugar. Cut in butter with pastry blender, fork or fingers until mixture is crumbly. Sprinkle over peaches.
Bake for 40 minutes or until peaches are tender and crumbs are golden brown. Serve with a scoop of vanilla ice cream. 6 or 8 servings.