Ordered Tolkien monster to swallow one horse up (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Ordered Tolkien monster to swallow one horse up GAN I (I + NAG (=horse); ”up” indicates vertical reversal) in ORC (=Tolkien monster, from The Lord of the Rings ); organic means structured, organised, hence “ordered”