We were given about 8 lbs of frozen goose breasts in a bag. I would think we can defrost it and will then have to cook all of it; slow cooker to be the best option.  Is there a method of cooking this goose? as I understand it needs to be cooked a long time to be tender. Can this be refrozen afterwards into smaller packages. We were thinking about cooking this for Christmas.  EDIT - The goose is skinless 
On many gas ovens, the calibration of oven temperature is fairly slack - the manual for mine says it can be off be 30 degrees either up or down. Invest in an oven thermometer, preheat your oven until it shows the desired temperature, and see if this gives you better results. 