In a bowl, toss your sliced rhubarb with 3/4 cup of the sugar and let stand for 15 minutes.
In a large bowl, toss your chopped strawberries with the remaining 1/4 cup of sugar and let stand for 10 minutes.
Preheat the oven 375°. Transfer the rhubarb to the strawberries, if your rhubarb produced a lot of juice carefully drain it out. Add your cornstarch, lemon juice and vanilla to the strawberry/rhubarb bowl and stir to combine. Pour the mixture into a 9x13 baking dish.
In the large bowl(it's okay to use the same fruit bowl), combine the "topping" ingredients; butter, maple syrup, flour, ground cinnamon, salt and quick cooking oats. Use a pastry blender, your fingers or a fork and mix the ingredients together until combined.
Sprinkle or scoop the topping evenly over the fruit filling. Bake for 30 minutes. Then reduce the oven temperature to 325° and continue baking for 30 minutes longer or until the fruit filling is bubbling and topping is nicely browned.
Let the crisp rest for at least 30-60 minutes before serving. Taste amazing the next day(or a few days later even).