Topping: Pulse sugar and molasses together in a food processor. Add flour, spices, and salt; pulse to blend. Add butter and pulse 10 times, about 4 seconds each pulse. the mixture will first look like dry sand, with large lumps of butter, then like coarse cornmeal. Add nuts, then pulse again, four to five times, about one second each pulse. Topping should look like slightly clumpy wet sand. Be sure not to overmix. Refrigerate topping while preparing fruit, at least 15 minutes.

Adjust oven rack to lower-middle position and heat oven to 375°. Combine fruit with sugar, lemon peel, and lemon. Scrape mixture into baking pan. Distribute chilled topping evenly over fruit.

Bake for 40 minutes. Increase oven temperature to 400° and continue baking until fruit is bubbling and topping turns deep golden brown, about five minutes more. Serve warm.