Kesler's apple rhubarb crumble

I made apple rhubarb 

Here's the ingredients:

3/4 cup sugar

3 tablespoons cornstarch

3 cups sliced fresh rhubarb or frozen rhubarb, thawed

2 cups sliced peeled apples or sliced strawberries

1 cup quick-cooking or old- fashioned oats 

1/2 cup packed brown sugar

1/2 cup butter,melted

1/3 all-purpose flour 

1 teaspoon ground cinnamon