Oats are Healthy, trying to find a replacement for them that is "healthier" is difficult near impossible.
The problem with oats and putting on weight is that they have a low calorie density and also are low GI. So you feel fuller for longer while only eating a little.
As someone who is going to want to be eating lots the low GI can make it a little difficult as trying to eat another big meal when already full is a struggle.
Personally I never gave up oats, my breakfast is normally 100g of oats with some toast (Grass-fed, unsalted butter) and a protein shake. You feel like you are going to explode and it takes a while to get used to it.
Then I go to the gym straight away and try to build up my appetite. Then have a post workout meal.
Again it takes time to adjust to eating lots but you have to be patient.
Try to make up the calories elsewhere because oats for breakfast is kinda amazing in every other aspect.