I use an apple crisp recipe and substitute plums for apples. Take about 3-4 cups of  previously  frozen, thawed plums. I like using frozen fruits as I find they are more flavourful. Add a handful of blueberries and thawed peaches if you have some on hand, You can increase the amount of fruit to cover an 8×8 baking pan about 1 1/2″ thick.

Sprinkle fruit with 1/4 c sugar and 1/2 tsp cinnamon.
Mix  together ½ c butter, 3/4 c brown sugar, 1/2c flour and 1/2 c rolled oats. Pat on top of fruit and bake at 350 degrees for 40 mins. i You can also add walnuts to create more texture).