done wet long and low - most cuts will come out tender.
couple of thoughts
easy - do you have a crock pot / slow cooker? that's the ultimate easy...
most of the flavor is going to come from the braising liquid and second from fat/connecting tissue of the meat.
lean cuts are not the best.
do you have a really sharp knife? for thin slicing, that's a definite need.
microwave reheating is not optimum imho - if for lunches that's the only possibility.... don't do at full power - try 30% power and a pause between heating times to allow the heat time to 'soak through' the meat hunk of the sandwich.
for seasoning I'm kinda' in the simpler is better camp.
salt, pepper/pepper corns, an onion product - or leeks (my fav), crushed garlic clove, diced celery/carrot
on the more exotic side, oregano, chervil, allspice, rosemary - not all in the same batch - and be aware some like rosemary a little bit goes a long way.