Preheat oven to 400°.
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. Sprinkle with oat mixture. Bake at 400° for 35 minutes or until bubbly.