I'm assuming you don't necessarily want a smoothie that's "workout" oriented but I drink these from time to time.
Half an avocado
1/2 cup of milk
1/2 cup of water
hand full of frozen cherries
scoop of vanilla protein powder
2 spoons of natty Peanut Butter
scoop of chocolate casein protein powder or whey. I drink before bed so I take the casein usually.