TOO-uh
It's a short, simple pronunciation with the emphasis on the first syllable.
Here's a breakdown:
* TOO: Pronounced like the English word "too"
* uh: Pronounced like the short vowel sound in "up" or "cup"
It's important to note that "Tuatha" is often part of a longer word, like "Tuatha Dé Danann" (pronounced TOO-uh DAY DAH-nann), which is the name of a legendary race of supernatural beings in Irish mythology.