Similar to the Ectomorph, the Mesomorph has a constitution which easily handles a higher calorie food-intake.
However, Ectomorphs may just have the edge when it comes to this characteristic. Nonetheless, Mesos don't really have to focus on nutrition to support lean mass gains, and so the emphasis for them is merely to ensure a wholesome balanced eating plan – mostly for maintenance.
If your desire is to add more muscle, then you simply need to boost your intake (proportionately) to support the required gains.
Although you have significant leeway in the eating department, you should still stick with a regular meal frequency to maintain your condition, and for optimal health.