0,5 L milk, one dose of protein powder and 100g of oatmeal mixed up in a blender was my go to breakfast for a while when i was trying to bulk. Blender grinds the oats to powder so its easy to drink. Ive since switched it up with other stuff and not trying to bulk anymore, but if i were to go back to it i think 30- 50g oats is just fine. If you want banana, eat it on the side cause it makes the drink thicker. Easier and faster to get the coctail down if its less thick, imo