As a former vegetarian, I can tell you that the reason veggies are usually grilled and rarely smoked is that the flavoring and tenderizing that smoking does to meat is not the same as what it does to vegetables.
But, a couple ideas:
Smoked stuffed mushroom caps - stuff cheese, spinach, and sautéed onions in mushroom cap and smoke until cheese is melted.
Smoked guacamole - Smoke all ingredients for an hour and then prepare as normal.
These are just off the top of my head. If I think of more, I'll add them to the list!