You can. While fresh is typically desired, using canned tomatillos can expedite preparation. Goya has both whole and crushed tomatillos in a 26 oz can - we'd recommend whole for this recipe - and you'd only need about half of the can. You can freeze the rest for another day. Add the tomatillos after you've cooked the onions down a bit, then carry on with the recipe as instructed below.