Mix together the vinegar, tamari, garlic and onion powders. Add the tempeh and toss to coat. Let rest at least 15 minutes, stirring occasionally to toss.
Heat oil in a skillet. Add tempeh and cook until it starts to brown and turn to brown the other side.
Serve the tempeh in wraps, on sandwiches, or in salads.
Notes
I usually get 25-30 slices, or 24 cubes off of an 8 oz tempeh block.