I simply cut everything up somewhat thinly, dredged it in a bit of oil and assorted spices, and then laid it on the rack. For the sweet potatoes, I did some just in oil, but then later added nutmeg or curry powder just to see what would happen. I did the same for the eggplant, but for the tofu I simply flopped it (gently) about in soy sauce and then put it on the rack. (As I finished roasting one thing and started the next I put it in a pan on the stove with a lid to keep warm.)
All of it turned out really well, although the tofu wasn't as firm as I would have liked. Even the firmest we've been able to find here is still quite soft, but we'll adapt. The sweet potatoes could have been a wee bit softer, but they were still quite tasty and the eggplant was perfect. We served it up with a little bit of wasabi on the side and a glass of cheap red wine. Yum!