A lighting fixture assembly for mounting to a structural body includes a mounting plate and a lighting fixture. The mounting plate has a lower side surface configured to receive the light fixture, and an upper side surface configured to mount to the structural body. The mounting plate has a recessed portion formed in a center portion of the mounting plate and extends longitudinally along the mounting plate. The recessed portion has a depth when viewed from the lower side surface of the mounting plate in a thickness direction. The lighting fixture comprises a chassis configured to be fixed to the mounting plate and one or more light sources mounted on the chassis. The depth of the recessed portion is equal to or less than a distance between an outer surface of the cover and an upper side surface of the chassis when viewed in the thickness direction.