Preheat oven to 400 degrees F. Combine the nectarines and blueberries in a medium sized glass baking dish. Sprinkle with the tapioca and add the honey and lemon zest. Mix well, making sure fruit is evenly distributed across the baking dish. Cover with aluminum foil and bake on center rack for 10 minutes.

While the fruit is cooking, make the topping. In a bowl, work the butter into the oatmeal using your hands. Stir in the brown sugar and cinnamon.

Remove the fruit from the oven, uncover and stir. Sprinkle the topping over the fruit and return it to the oven, uncovered. Bake 15 to 20 more minutes, until the topping is browned. Serve warm.