Cook the onions in cooking oil to simmer.
Heat the cooking oil in a large pot set over medium-high heat. Sauté the onionin the oil, stirring often, until the edges begin to brown, about 5 minutes
Add the turkey legs, smashed garlic, chicken stock, and water, and bring to a simmer.
Cover and cook for 1 hour.
Add the collard greens and cook, partially covered, until they are tender, another 45 minutes to an hour.
Chop the meat, add to the greens.
To serve, remove the turkey legs, pull the meat off the bones and chop. Mix the meat back with the greens.
Season the collards, then serve.