It's difficult to find a good meaning for the 3NT opening. The "natural" strong balanced meaning doesn't work very well because there's too little space to bid constructively over it. More often 3NT gets used as showing a pre-empt in one of the minors, either "Gambling" (promising a solid suit) or showing a normal 4-minor pre-empt so that the 4C and 4D opening bids can be used for other purposes. However, this wrong-sides the possible 3NT contract, and, particularly when 3NT does not promise a solid suit, it can be difficult for partner to know whether to play in 3NT anyway. Also, using 3NT for any sort of pre-empt gives the opponents more options than they would have if you had made a natural opening bid.
I prefer to use 3NT to show a hand which is not interested in playing in no-trumps at all. One possibility which a few pairs have adopted is to reverse the usual "Namyats" opening bids so that instead of 3NT showing a minor-suit pre-empt and 4C/4D showing good major-suit pre-empts, 4C and 4D become natural and 3NT shows a good pre-empt in either major suit. This seems like a reasonable thing to do. But what I would like to recommend is the simpler approach where 3NT shows specifically a good pre-empt in hearts.
You make life a lot easier for yourself by showing a specific suit. As I said here, I'm generally wary of agreeing to play multi-meaning pre-empts because there is so much which needs to be discussed. Also, slam tries are more effective when the suit has already been shown because you don't need to waste time confirming which suit opener has.
Of course, this gives up the chance to show a good 4S pre-empt. But there are good reasons why being able to show hearts is more important than being able to show spades. When you have hearts, you are worried about the opponents competing in spades. You want to make a pre-emptive bid to keep them out of their possible good spade fit - or to put them into a bad spade fit. And also if you open at a lower level you might get pre-empted yourself. For example, if you open 1H, the opponents may be able to bid up to 4S and leave you unable to show your one-suiter without going to the 5-level. When you have spades you are less worried about keeping the opponents out since you can outbid them on any level. Note also that a 3NT opening prevents the opponents from bidding spades below the 4-level, the same as a 4H opening would. If you have spades, then an opening bid which shows a good 4S pre-empt will allow the opponents to get in a heart bid at the 4-level, so this is significantly less pre-emptive than a 4S opening would be.