Peanut Butter and Banana smoothies are pretty common these days. The first time I tasted one was at a local vegetarian, organic restaurant called The Green Theory. Their smoothies are more like milkshakes - decadent, creamy and well, fattening (hey, I'm not complaining :D). If you let them know in advance that you'd like your smoothies to be made with soy mylk (instead of animal milk), they usually oblige.
Bikash Parik, who owns the restaurant, is a really nice guy and very helpful and accommodating. I've seen him there almost every time I've visited. He's the tall guy wearing the glasses. If he's around, then it's a guarantee that you'll have a good, vegan dining experience after explaining to him that you're vegan upon entering the restaurant.
Coming back to my smoothie, I personally feel that a smoothie doesn't need any sort of mylk to be added. Especially not one with peanuts or bananas in it. You have all the creaminess required right there, in those two ingredients. Here's my version of the Peanut Butter and Banana smoothie. I added a small pinch of a special ingredient to give it a more Indian flavour. Hence the 'fusion' in the title. :)
1 big scoop of Peanut Butter
1 large, ripe Bananas (the Pachbale kind) - peeled and cut into large chunks with a few small slices kept aside for topping
4 Dates - seeds removed
2 tsp Sugar (optional for additional sweetness)
1 T Cocoa Powder (optional)
A pinch of Pachha Karpura (Edible Camphor)
A pinch of Salt
Blend everything (you can adjust thickness with a little water if you like).
Serve into tall glasses.
Top with banana slices.
Dust with cocoa powder.