How to get to 4 Hearts rather than 3NT if the opponents don’t overcall their spade suit?

Bernard's Answer

N opened 1 club, E: P, S bid 1 Diamond, W: P, N 1NT to show 15 and balanced, S bids stamen 2Clubs, N responds 2D, and S raises to 3NT with the immediate loss of 5 spade tricks. How should we have avoided this?