In a small bowl, stir together bragg's amino acids, apple cider vinegar maple syrup, cumin, paprika and chili powder. Pour over tempeh slices, cover and chill 2 hours, or overnight.
Preheat oven to 300°F. Line a baking sheet with parchment paper. Carefully transfer tempeh slices to prepared baking sheet, and discard marinade.
Bake 10 to 15 minutes, or until beginning to brown. Flip tempeh slices and bake 5 to 7 minutes more, or until crisp and dark brown.
Assemble sandwich using toasted bread, avocado, lettuce, tomato, vegan mayonnaise and enjoy :)