In medium bowl, toss together all fruit base ingredients. Transfer to a lightly greased 8x8" or 9x9" baking dish.
In the same bowl, melt butter. Add all other topping ingredients and mix with your fingers until well combined and crumbly. Sprinkle evenly over top of the fruit.
Bake for 35-40 minutes, until fruit is tender when pricked with a fork and topping is toasted and golden.
Best served warm or room temperature with ice cream.
Notes
*If making this for gluten free diets, ensure your oats are certified gluten free. Some oats are cut with flour and it may not be listed on the ingredient list of the bag.
Recipe by Hidden Ponies at https://hiddenponies.com/2012/08/saturday-sweets-apple-rhubarb-crisp-gluten-free/