Although turians have a strict moral code, their belief in individual responsibility means that the concepts of good and evil are simply the individual's choice between egotism and altruism in any given decision. They have no concept of "good" deities that encourage noble behavior or "evil" ones that tempt individuals to misdeeds.
Turians believe that groups and areas have "spirits" that transcend the individual. For example, a military unit would be considered to have a literal spirit that embodies the honor and courage it has displayed. A city's spirit reflects the accomplishments and industry of its residents. An ancient tree's spirit reflects the beauty and tranquility of the area it grows within.
These spirits are neither good nor evil, nor are they appealed to for intercession. Turians do not believe spirits can affect the world, but spirits can inspire the living. Prayers and rituals allow an individual to converse with a spirit for guidance or inspiration. For example a turian who finds his loyalty tested may appeal to the spirit of his unit, hoping to reconnect with the pride and honor of the group. A turian who wishes to create a work of art may attempt to connect with the spirit of a beautiful location.
Turians enjoy absolute freedom of religion and can practice whatever appeals to them so long as it does not impede anyone's ability to perform their duties. There are many practitioners of the asari "siarist" philosophy. Since opening dialog with the human Systems Alliance, some turians have embraced Confucianism and Zen Buddhism.