Prep the tempeh. Slice it into strips as thinly as you can. Then mix the balsamic vinegar & teriyaki in a medium bowl, and marinate the tempeh in the mixture for about 30-45 minutes, or until you can see that the tempeh has soaked up a lot of the marinade.
As the tempeh is marinating, slice the onion and green bell pepper into long strips and slice the mushrooms, like you would for a Philly cheese steak.
When the tempeh is ready, heat a saute pan to medium-high, and add the olive oil. Then saute the onions, peppers, and mushrooms until they begin to caramelize. Now add the tempeh. It will probably crumble, but that's ok. Then add the Rogan Josh spice, salt, and pepper to taste.
Slice the hoagies lengthwise if not already sliced, and toast the inside portions under the broiler until light golden brown. Then spread the vegan mayo to taste on the bottom part of the bread, pile on the sauteed veggies, and top with the vegan cheese. Then put those bottom portions back under the broiler to let the cheese melt.
Assemble the sandwiches and you're ready! These are great with some chunky steak fries!! I served this to non-vegetarians, and they were very pleasantly surprised! Yum-Yum!