Well the show has a lot of Indian references:
In Hinduism Vishnu,God of preservation has taken 10 Avatars for the protection of the good and for the destruction of evil, and for the establishment of righteousness. The 9th Avatar was BUDDHA who was founder of buddhism. Initially it was just a branch of hinduism and later separated so Buddhism has most of the things derived from Hinduism. Buddhism was born in India and travelled to rest of the world. (10th avatar is yet to born)
Avatar, Raava, Vaatu, Bumi, Opal, Salai, Agni, Guru (all Sanskrit, although "Opal" is westernized), Pathik, and Kuvira (both hindi).
In the classic Hindu Epic Bhagavad Gita prince Arjuna prepares to engage in legendary battle of Mahabharata when he realizes that the opposing army is populated by many of his friends and relatives, and thus becomes conflicted about fighting, despite being aware of their evil. The arguments that Krishna (Avatar of Lord Vishnu, God of Preservation) gives to prince Arjuna in favor of participating in the battle are very similar to the arguments that the past Avatars give to Aang, like Kuruk's advice on the consequences of inaction and Kyoshi's alluding to a greater good that would outweigh the evil of taking life.
The firebending third eye of Combustion Man and P'Li resembles the third eye of Lord Shiva, the Hindu God of Destruction.
In Hinduism's sacred literature, the "great" or "gross" elements (mahābhūta) are fivefold: ether, air, fire, water and earth from which the show is inspired.
In Hinduism Lord Vishnu's Avatar Kurmaraja is a tortoise which is very similar to the lion turtles and their original work of protecting mankind.
My theory
The lion turtle which gave Aang energybending was an Energy turtle just like fire turtles ,water turtles, earth turtles or air turtles. It can be that some people continued to live on the energy turtle, people with most similarities to the Indians. Around 150 years ago when all other turtles were already hunted and killed, our turtle was attacked. Most humans died protecting the turtle from elementbending hunters as they were all nonbenders. At last the lion turtle some how reached one of the air temples. The air benders helped the lion turtle. But could not save all the Indian-like people except one. The turtle gave the one energy bending and left him to live with the air nomads. The child was Pathik who travelled and learned spiritual stuffs from the nomads and became a guru. Thus he was spiritual brother of air nomads, personal friend of Gyatso (and maybe even spiritual mentor of Iroh and member of white lotus). He survived the 100 year war and helped aang. It is possible that it was he who sent the Lion turtle to Aang as he most probably knew that Aang had locked his chakra.