Preheat oven to 400 degrees.
In a large bowl, gently stir together the peaches, pineapple juice or lemon juice, brown sugar, cornstarch, vanilla extract, and cinnamon. Spoon into a 9 x 9 inch or equivalent size baking dish.
Whisk together flour, brown sugar, cinnamon, and salt. Using a pastry blender, cut in butter until crumbly. Stir in the oats.
Bake for 30 minutes or until the fruit is bubbly and the top is golden brown.