Recently, I was dealt a hand with a high card point and distribution too strong to open 1 NT but not enough to bid 2 of a suit, i.e. in "no man's land". Any advice you can provide about how I should open the bidding with such a hand would be much appreciated.
A hand "too strong to open 1 NT but not enough to bid 2 of a suit" is of two possible ranges of interest: 18-19 and 20-21. If we are talking a balanced hand with (according to the most common partnership agreements) at worst Kx or Qxx in every suit:
If the hand is unbalanced then it opens one of a suit and either jump-shifts as a rebid with 20+ points, or reverses as rebid with 18+.
Don't get in the habit of opening hands 1NT that are unsuitable for notrump play, just because they fall in the 15-17 point range; you sill seriously stunt your development as a bridge player, and alienate potential partners. There is a very good reason why Victor Mollo called the member of his menagerie prone to such bids the Hideous Hog.
As strong as your hand is, it is not strong enough to do much unless partner responds. Once that happens, you have probably the makings of a potential game contract if there is a fit.
One problem with the description of your hand is that it encompasses a fairly wide range, from 18-21 high card points (HCP).
With 18-19 points, I would bid one of any five card suit, especially a five card major, but one of a "short" minor otherwise. This allows partner to respond with 1 at a higher suit, or 1NT, showing at least 6 HCP.
If partner responds "one over one," you can go to 2NT with a balanced hand. Partner will raise you to 3NT (or four of a six card major suit) unless he has the bare minimum 6-7 HCP, in which case he will sign off by passing or going to three of his suit.
If you had bid a five card major, and partner raises to two, you should raise to three. Partner will take you to four with anything more than 6-7 points.
With 20-21 points, you open directly with 2NT, assuming that the hand is balanced. If it's unbalanced, bid one of a suit, as above, and then "play it by ear." Use "strength showing bids" such as jump shifts or reverses to show your extra values. Partner will take you to game unless he has the bare minimum 6-7, or there is a misfit.
If partner shows a suit at the one level (four cards and at least six HCP), you can go directly to 3NT with 20-21, and a balanced hand.