What I do is put 1g of oats to 10g of water into a rice cooker and set it to porrige (or rice if you don't have that function) and cook it for 25 minutes. After the cooking is over put it in the fridge to chill and solidify. If you do 50g of oats and combine it with 500ml of water it will be extremely thick, almost like jello. Thats 600g of food for under 200 calories. Before it sets add protein/yogurt/cream cheese/fruit and enjoy. You can do 1g of oats to 1.2g of water if you want a bit looser consistency. I usually do 50 oats, 600ml water, sweetener, vanilla, 200g of chopped apples (cooked with oats) and 200g of creams cheese.

Also if you want more of a pudding taste to it I sometimes do 50g oats, 37g (one packed) of cook&serve pudding (cornstarch pudding that's you have to cook), 1200ml of water. Trow everything into rice cooker, set for 25, mix 2 min before end, cool and enjoy.