Mix the blueberries, sugar, and lemon zest in the baking dish and spread in an even layer.
Make the topping: mix the flour, oats, brown sugar, and cinnamon in a bowl. Cut the butter into small pieces and toss with the dry ingredients. With your fingertips, work in the butter until the mixture is crumbly. Add the almonds.
Sprinkle the topping evenly over the berries.
Bake for 30-40 minutes, until the top is golden brown and the juices are bubbling.