Preheat oven to 350°F. Grease a 9 inch baking dish with cooking spray.
In a bowl, combine the flour, brown sugar, oats, ginger, salt and cinnamon. Add the melted butter and use a fork to combine until mixture is crumbly. Set aside.
In another bowl, combine the ricotta cheese, ¼ cup (50 grams) of the sugar, and the vanilla. Set aside.
Toss the sliced rhubarb with the remaining ¾ cup (150 grams) sugar and the cornstarch in the baking dish. Spoon the ricotta mixture over the top. Sprinkle with the oat crumb mixture.
Bake until bubbly around the edges and topping is golden brown, about 20 minutes. Serve warm or at room temperature.
Store tightly wrapped in the fridge for up to 3 days.