This is a favorite of ours.

1/4 cup of real oats. Not quick oats
1/4 cup of milk (I use whole milk)
1/4 cup of plain Greek yogurt
Half a diced banana
1tsp vanilla essence
Sweetener of your choice. (I use equal)
I scoop of protein powder

Mix all ingredients together
Pour into air tight container (I use mason jars)
Refrigerate overnight.