I have a recipe for spring rolls which call for (essentially) half watercress and half ground pork.  I boil the watercress first, then chop it and fry it with carrot, tofu, and seasonings.  Then I add the meat (cooked previously).  Often when I make the recipe I am half-way through (or worse) and I realize that the watercress is way too bitter to eat.  I'm not sure why this is happening; it could be the watercress itself or perhaps I didn't boil it long enough.  What tips do you have for preventing this situation, and is there a way to fix this dish? I'm willing to add anything, even if it changes the flavour a lot, to rescue this dish. 
Don't boil the watercress, just wash and use raw  I suspect the Asian watercress varieties are a little hardier than what is found in most western countries  You could try substituting it with some other Asian greens. Maybe a mix of Choy Sum and Coriander with some grated White Turnip for some peppery zing. Or try other peppery greens like Arugula, Endive, or whatever local weeds provide that peppery taste (Daisy family?) 