Now this is a sandwich!
Preheat the oven to 190/370deg.
Slice the tempeh into 1/4-inch-thick pieces and set aside.
In a small bowl, combine the sesame oil, shoyu, hot sauce, (if using) garlic cloves, ginger and juice from one lemon. Whisk to combine and transfer to a large, zip-closed plastic bag.
Place the sliced tempeh in the bag and gently massage it with your hands to coat all the pieces. Refrigerate for 30 minutes.
Remove the tempeh from the marinade. Grill for 10 minutes, turning half way until crisp and golden.
Serve on granary bread spread with vegan mayonnaise, add shredded lettuce, cucumber, tomato slices, avocado slices, place two pieces of the crispy tempeh and top with some onion relish.