Preheat the oven to 350 degrees. Gently mix the fruit, agave nectar, lemon peel and corn starch until the corn starch has dissolved. Spoon this into a 9x13 inch baking dish.
Mix together the flour, oats, wheat germ and salt. Cut in 5 tablespoons of the butter till the mixture resembles coarse crumbs. Stir in the agave syrup with a fork. Toss it evenly over the fruit and dot the top with the remaining 3 tablespoons of butter.
Bake for about 35 to 40 minutes. The streusel should be golden brown and the fruit bubbling and somewhat thickened.