Preheat oven to 350°F and lightly coat a 2-quart casserole dish with nonstick spray or butter.
In a bowl, combine rhubarb, sugar, and flour. Stir to coat evenly, then set aside while you make the topping.
In another bowl, combine oatmeal, flour, brown sugar, almonds, ginger, cinnamon, and salt. Stir to evenly distribute, breaking up any chunks of brown sugar. Add the melted butter and stir until no dry bits are left and topping is forming clumps.
Scoop the rhubarb into the prepared baking dish. Scatter the crisp topping evenly over the rhubarb. (You might not want to use it all. Save any extra for another recipe.)
Bake for 40-45 minutes, until topping is browned and crisp and fruit juices are bubbly. Let cool at least 10 minutes before serving.
Notes
Use the lower end of sugar for a more tart crisp.
Extra crisp topping can be stored in the freezer for 3 months.