Last weekend I went to this potluck-style vegetarian barbeque with 20+ vegetarian and vegan participants. A very nice affair, with lots of very nice food demonstrating that vegetarians don't need to suffer at barbeques.
As I had been a little late to claim a specific dish, all the obvious things (tofu and veggies on skewers, salads, vegetable packets) were already accounted for, so I decided to try my first thought: something that would be somewhat like spare ribs (which I'd enjoyed before becoming veg(etari)an). As tofu seemed to be well-represented already and tempeh just marinates better and is firmer, I thought I'd try the latter. I googled for a recipe for tempeh in BBQ sauce and took it from there...
They turned out quite well.
How I did it (and stopped worrying about the measurements)
1 pound (450 grams) of tempeh, in 1/4 inch (0,5 cm) thick slices
1/2 of a small onion, finely diced
2 cloves of garlic, minced
1 teaspoon of ground cumin
1 teaspoon of ground coriander
Dried chili flakes, cayenne
Lemon juice (concentrate will do)
4-5 tablespoons of neutral oil (sunflower oil)
Fry the onion and garlic in the oil. Briefly fry the spices before adding a lot of ketchup (half a cup, 100 ml) and molasses, soy sauce and lemon juice. Let it amalgamate on medium heat for about 10 minutes and keep tasting while adding molasses, soy sauce and lemon juice to get the taste you like, and a bit of cayenne for additional heat. I guess basically you're playing with most of the basic flavors here. Molasses for sweet, soy sauce for salty and umami and lemon juice for sour. Season with salt. Layer the slices of tempeh in a container and pour over the marinade. Cover and put in the fridge to marinate for a night and cook them on the barbeque. They will need about 10 minutes, with some turning.
You could probably also bake them for about 12 minutes in an oven at 350 degrees Fahrenheit (180 degrees Celcius).
The recipe I had found also called for mustard, but I forgot to add it. You might try it, I certainly will next time.