I am assuming the Stonewall Attack is from White. I would think the best way would be to set up a financhetto on the kingside for Black. That should blunt White's attacking Bishop on d3. Other methods may be to successfully occupy the square on e4, also trading Bishops on f5 may work even if the f-pawns are doubled.
I know from experience that this attack can often be successful against unprepared players.
I think GM? Sam Shankland had a video about offbeat queen pawn openings and he covered the Stonewall Attack.
What is the best way to play against the Stonewall Attack?