The present disclosure is directed to a combustor assembly for a gas turbine engine. The combustor assembly includes a deflector wall, an annular axial wall, and an annular shroud. The deflector wall is extended at least partially along a radial direction and a circumferential direction relative to an axial centerline and adjacent to a combustion chamber. A fuel nozzle opening is defined through the deflector wall, and a nozzle centerline is extended through the fuel nozzle opening along a lengthwise direction. The annular axial wall is coupled to the deflector wall and extended through the fuel nozzle opening. The axial wall is defined around the nozzle centerline. The annular shroud is defined around the nozzle centerline and extended co-directional to the axial wall. The axial wall and the annular shroud are each coupled to a radial wall defined upstream of the deflector wall. The annular shroud, the axial wall, and the radial wall together define a cooling plenum therebetween. The axial wall defines a discrete inlet opening therethrough providing fluid communication from a diffuser cavity to the cooling plenum. The cooling plenum defines an exit opening providing fluid communication from the cooling plenum to the combustion chamber.