Lightly spoon flour into a dry measuring cup; level with a knife.
Combine flour, brown sugar, and almonds in a food processor; pulse 5 times or until blended.
Add oats, butter, cinnamon, and 1/4 teaspoon salt; pulse 5 times or until mixture is crumbly. Set aside.
Combine plums and remaining ingredients except cooking spray in a large bowl; toss well. Spoon plum mixture into a 13 x 9-inch baking dish coated with cooking spray.