Prepare syrup by heating equal parts sugar and water, along with vanilla bean and lemon juice.
Once sugar has dissolved, cook the rhubarb in syrup until soft. Strain and let cool. Mix cooled rhubarb and strawberries together. Add dry ingredients, as well as lemon zest and juice. Spoon mixture into individual oven-safe dishes.
To prepare topping, mix butter and sugars together. With your fingers, add flour, oatmeal, vanilla and salt until it crumbles. Do not over mix. Crumble topping over each of the fruit dishes. Bake at 350°F (175°C) until topping is light brown.
Serve with crème fraîche or vanilla ice cream.