Various representative commercial cooking devices are disclosed wherein a recirculating flow of heated air, at a food cooking temperature, is created within a housing in which a horizontally disposed food support and cooking member, such as a perforated metal plate, a solid griddle plate or a metal broiling grate, is positioned. A plenum structure is utilized to convert a portion of the continuously recirculated air into a spaced series of relatively high velocity heated air impingement jets which are caused to laterally diffuse and at least slightly overlap prior to striking at least one side surface of the food support structure. In this manner, each food support structure side surface subjected to such diffused jet impingement is evenly blanketed with heating air to thereby very uniformly transfer heat from the air to the food support structure, and thus to the food supported thereby, at an accelerated rate.