In a medium bowl, combine strawberries, apples, lemon juice, vanilla, cornstarch, cinnamon, salt and sweetener.
Stir until everything is mixed together and there are no dry bits. Set aside.
For the crumble
In a large bowl, combine sugar and flour. Dice the butter into small pieces and toss in the flour and sugar mixture.
Cut the butter into the flour and sugar with a pastry cutter or use a fork until the butter pieces are the size of peas or the mixture looks like breadcrumbs.
To assemble the strawberry and apple crumble
Fill the ramekins with the fruit mixture (about 1/2 cup each). Firmly pack down the fruit to ensure the whole dish is covered. The fruit shrinks when cooked.
Cover the fruit with a thick layer of the crumble.
Bake at 350 for 25 minutes until the fruit mixture is bubbling though the top.
Let chill for 15 minutes before serving by itself or with vanilla ice cream.