Mix the berries, sugar, lemon juice and zest, and flour in a large bowl. Preheat the oven to 400 degrees F, and butter a 13x9-inch glass or ceramic baking dish.
For topping: Combine the flour, brown sugar, oats, cinnamon, and salt in the bowl of a food processor. Add the butter, and pulse the machine repeatedly, in 2- to 3-second bursts, until the mixture is clumpy, like damp crumbs. Transfer the berries to the baking dish, and spread the crumbs evenly over the fruit. Bake for 30 minutes, until bubbly hot. Serve at any temperature, although it is best to let it cool at least 10 minutes.