Oats are ok for bulking up. Eating a load more oats will give you loads more cals but tbh... i'd rather get the cals from protein where possible, to try and avoid fat gain as much as i can.
So, if i was you i'd try and get the extra calories from lean meat aswell as oats and carbs. i.e. add in another 500-700cals a day but make those cals up from 60%/30%/10% in terms of protein/carbs/fat.