Place blueberries in a nonreactive mixing bowl. Add ¼ cup flour, sugar, lemon zest, and lemon juice, then gently toss to mix. Spoon mixture into aluminum-foil pan after lightly spraying it with cooking oil.

Place biscotti or gingersnaps, brown sugar, and remaining ½ cup of flour in a food processor and process until a coarse powder forms. Add butter and salt, then pulse until crumbly. Spoon the topping over the blueberry mixture.

Set up the grill for indirect grilling and preheat to medium high. If using a gas grill, place all of the wood chips in the smoker box and run the grill on high until you see smoke, then reduce heat to me-dium high. If using a charcoal grill, preheat it to medium high, then toss all the wood chips or chunks on the coals.

Place the pan in the center of the hot grate, away from the heat, and cover the grill. Cook until the blueberry mixture is bubbling and the topping is browned, about 40 minutes. Serve with vanilla ice cream, if desired.