This is the healthy version I pulled off grouprecipes.com. It's also the easiest to make, BUT it requires an ice cream maker, and even then it has a tendency to get a little hard which personally doesn't bother me.
2 boxes silken tofu
2 1/2 c. plain soy milk
2/3 c. honey
4 tsp. Matcha powder (powdered green tea)
1/2 tsp. Vanilla
Whisk the soy milk and matcha powder first to make sure the powder gets dissolved and then evenly distributed throughout the ice cream. Dump it into an immersion blender/blender/processor with the rest of the stuff. Blend until everything is all mixed up together into one smooth mixture. Pour into ice cream maker of your choice. Make ice cream like usual. Leave it in a little extra long if possible. Pour into container and freeze overnight.
This is the unhealthy, messier and slightly-harder-to-make (but still easy) version that does NOT require an ice cream maker and also tastes better:
3 egg yolks
1/4 to 1/2 cup sugar (depending on how sweet you like it)
2 TBS green tea powder (Matcha)
1 1/4 c heavy cream
I am lazy, so I substitute honey for sugar (blends easier). I whisk the green tea powder with the cream then dump everything in a food processor/blender/immersion blender. You can also add a bit of vanilla or ginger or cinnamon or whatever to suit your taste.
You have to have a pretty good immersion blender or processor to get everything to blend properly. If you do not have very good blender, you can add a tiny bit of water to the green tea first, then mix that all up. Then take the yolk, cream, and sugar and put it on very low heat and whisk that all up. Then add the green tea paste to the ice cream base and whisk that all up.
Pour mixture into container (metal is preferable because of the freezy properties of metal). When it's hard and just about frozen (but not so hard you'll break your blender) take it out of the freezer and dump it into your processor. Mix it all up again until it is soft-- like really soft soft-serve ice cream, but not liquid. Put back in freezer.
You can repeat the process several times (and you may have to if you overliquify). Also depending on how hard you like your ice cream. The freeze-then-process procedure is basically just high-tech ghetto churning. You just want to make sure you don't break your processor. If it gets too hard, you can always melt it a bit, process it, and refreeze. If, after like 6 hours and you've gone through the process 2 times already then you need to let it sit longer and churn less.