Slice tempeh into ¼ inch slices, cutting strips from the shorter side versus the longer edge. Place in shallow dish for marinating.
Combine maple syrup, molasses, liquid smoke, nutritional yeast, Tamari, apple cider vinegar and garlic powder in measuring cup. Whisk until combined, then pour over tempeh strips.
Make sure all the tempeh pieces are covered in marinade, then place in fridge and let sit for 30 minutes.
Heat oil in a large skillet. Once hot, carefully place tempeh slices into pan, cooking until golden brown on both sides, about 3 minutes per side.
Remove tempeh from pan and place on paper towels to soak up any extra oil.
To serve, slather toasted bread with vegan mayo and top with tempeh strips, avocado slices, tomato, and romaine.