In a blender, whirl lavender and tapioca until finely ground. Pour into a large bowl. Stir in 3/4 cup sugar and the cinnamon. Add blueberries, raspberries, and lemon juice; mix gently. Pour into a shallow 2 1/2- to 3-quart baking dish.
In a food processor or bowl, combine flour, remaining 1/2 cup sugar, and butter. Whirl or rub in with your fingers until coarse crumbs form. Stir in almonds. Squeeze handfuls of the nut mixture together, then crumble into about 1/2-inch chunks over fruit mixture. Set dish on a foil-lined baking pan.
Bake in a 350° oven until juices are bubbling in the center and streusel is browned, 60 to 70 minutes. Cool on a rack at least 45 minutes. Serve warm or cool. Spoon crisp into bowls.