Pre-heat oven to 375 degrees F.
Toss frozen cherries and peaches in fresh lemon juice. Then sprinkle the fruit with flour and cinnamon. Toss to coat.
Place fruit mixture into a rectangular glass baking dish (8 x 11 inches).
Bake at 375 for 10 mins. (If using fresh fruit, you can skip this step).
While the fruit mixture bakes, in a large bowl add cubed butter, oats, brown sugar, cinnamon and salt.
Using 2 knifes "cut" through the mixture, combining the ingredients together.
Keep going until a good crumble is formed and the butter chunks are well incorporated into the oats.
Take the fruit out of the oven and add the oat crisp topping overtop all of the fruit.
Bake for another 20 minutes in the oven. Crisp will be hot and bubbling at the sides when done.
Serve warm.