The invention pertains to an accessory for adapting cooking grills, especially kettle and kamado style grills for better cooking of pizzas and other foods not typically thought of as appropriate for grilling. The accessory is an insert that is adapted to sit between the bottom and the top of the grill and is generally shaped with a horizontal cross-section substantially similar to the horizontal cross section at the junction of the bottom and the top of the grill with which it is adapted to work. The insert increases the height of the cooking chamber. The insert includes a side opening or window through which food may be inserted and removed from the expanded cooking chamber without the need to open or remove the top of the grill.