It comprises an inner wrapper which contains the food product, an outer package of plastic material which encloses said inner wrapper, a layer of a heat-concentrating material, arranged adjacent the inner wrapper, and a substrate attached to an outer face of said outer package. The layer of heat-concentrating material causes the opening of the outer package by melting a portion thereof, during heating of the assembly in a microwave oven, and the substrate prevents the outer package from sticking to the base of the oven. There can also be a sheet of insulating material between the inner wrapper and the outer package. Handling operations are reduced and the protection and optimum degree of humidity are maintained until the time the product is put in the oven.