Step 1: Char-Coal!! FIRE FIRE, hehe, FIRE!
Let the charcoal burn up for at least 30 minutes so there is no flavor from the fluids left, and to maximize the heat.
Step 2: Prep the tomatoes, and hydrate your wood.
I chose to leave the core/stem because I am going to roast them upside down and didn't want the moisture to escape. I guess you could do it either way.
Also, if you want some smokey flavor, you should get your favorite wood of choice and hydrate them in warm water for at least 20 minutes. This prevents them from just burning up. I used oak chips that are typically used for wine, but it's all I had laying around.