Collard Green Gumbo with Ham Hock

2 tablespoons vegetable oil
1 large onion (peeled and diced)
3 celery stalks (chopped)
2 cloves garlic (peeled and minced)
1 teaspoon dried thyme
1/2 teaspoon chopped red pepper flakes
1/2 teaspoon salt
1/2 teaspoon dried oregano
2 tablespoons whole wheat flour
4 cups water
6 cups chopped collard greens
2 ham hocks
2 cups cooked brown rice

Put a skillet on the stove and turn the heat to medium. When it is hot, add the oil. Add the onion, bell pepper, celery, garlic, thyme, red pepper flakes, salt, and oregano, and cook until golden, about 20 minutes.
Add the flour in small amounts, sprinkling a little bit at a time and stirring well, until it turns slightly brown, about 10 minutes.
Slowly add the water, stirring constantly. Add the ham hock. Raise the heat to high and when it comes to a boil reduce heat to low.
Add the collard greens and cook until tender, about 45 minutes.
Divide the brown rice between 4 shallow bowls and top each with about 1 cup of gumbo.