The most common and most likely answer to this crossword clue is the 12 letter word HAPPY-CLAPPY
I've seen this crossword clue in The Guardian
H
A
P
P
Y
-
C
L
A
P
P
Y
Buddy explains!
The straight part
We know that "Evangelical" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case evangelical = happy-clappy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HAPPY-CLAPPY mean?
HAPPY-CLAPPY noun- A member of a Christian church whose worship is characterized by enthusiasm and spontaneity.
- Of or relating to such a worshiper or such a church.