1/2 cup roughly chopped pecans
1/2 cup rolled oats
1/2 teaspoon cinnamon
3/4 cup flour
1/2 cup light brown sugar
1 tablespoon sugar
6 tablespoons unsalted butter

2 1/2 pounds plums, quartered and pits removed
1/2 cup sugar, plus 2 tablespoons
3 tablespoons all-purpose flour

Preheat oven to 400 degrees F.
Set rack in the center of the oven. Combine all of the topping ingredients into a food processor. Pulse until the mixture forms crumbles the size of small peas; do not over process. Set aside.
Pour the plums directly into a large, shallow baking dish and sprinkle with sugar and flour to coat evenly. Spread crisp topping over entire surface of fruit. Bake until fruit is bubbly and the top is golden brown, approximately 30 to 40 minutes. Serve warm or room temperature.