After reading responses I've gotten Belize and Fiji are coming up strong.
Scuba Board did a group trip, called an Invasion, to Fiji in 2019 and
that forum section should have a lot of info. you can use. Other than knowing it's farther afield than the Caribbean and said to be big on soft corals and a great destination, I don't recall much about Fiji and have never been.
I've been to Belize via live-aboard (and on a cruise ship stop), but you don't likely take a non-diver on a live-aboard trip. Belize is not an island, it's a nation, and has diverse offerings but confronts you with choices. The best diving is said to be farther out (hence the popularity of far atolls like Turneffe for land-based trips, or live-aboard trips). When you research it on the forum, I think you will see some main themes:
1.)
Ambergris Caye - large, long island near the mainland that I take it is touristy, and a good base for people who want to dive conveniently but do other things, too.
2.) Caye Caulker - island that's more rustic/laid back, likely not what you're looking for (I'm guessing) but you'll see it mentioned.
3.) Turneffe Atoll - farther from the mainland, a resort here can be pricy, maybe better diving.
Turneffe Island Resort.
4.) Mainland Belize - Has a lot of non-diving things to do; I really enjoyed a cruise excursion by boat up the New River to walk the rain forest and visit 3 (and climb atop 2) large Mayan ruins. For a mainland-based trip, I've seen
Splash Diver Center in Placencia repeatedly praised.
5.) Belize City has a reputation for being 'rough' in places. I doubt you will want to spend a week based right in it, but read about in on forum threads and judge for yourself.
Other people can give you way more first-hand info. on those options; I thought a cursory overview might help get you started searching, if Belize is the place you want to be.