Which workout routine is the best for gaining muscle mass?

I already have an eating routine that will help me increase my weight, but I just don't have a workout routine that will help me gain mass. I just want a 3 days routine that help me gain mass, whether it be a full body workout or a split body workout. I just need a workout that is efficient and will show results. My diet is under control and I know what and how much to eat, but it just seems that my workout plan isn't working out. Thanks for the help, I just need some direction on which workout routine would be helpful.