This is something that I made that actually tasted really good! It might also be good with mushrooms.
Heat Olive oil in skillet. Add chopped onion and cubed tempeh and saute until it starts to brown. Add salt, pepper, and garlic and a little bit of water until it is a little soupy. Cover and let simmer while you chop up the tomato. Add tomato chunks, cover, and let simmer until tomatoes are a little limp. Add a little bit of cornstarch/water mixture so that it thickens.
Delicious!