I was using the shadow dragon and moved three squares and I was one square short of a door I wanted to open, normally not a problem as I could expand into that square, however a hero figure was in the way and I couldn't expand, if I could have opened the door I would have been able to expand into that space. I wasn't sure how to play this as the rules say you can interrupt movement to perform an action, but I guess expanding into a space is ending your movement and at that point I could not expand into the space without the door being open. I played it like that.
p.16 "When the monster ends (or interrupts) its movement, the overlord player places the large monster figure ... if the monster cannot fit its entire base on the map, then it cannot end (or interrupt) movement in that space."
So, if I'm reading your post right, no. You wanted to interrupt your movement to open the door, but there was no legal placement of the figure. So you could not interrupt your movement adjacent to the door to open it.