Place the black-eyed peas into a large container and cover with several inches of cool water; let stand 8 hours to overnight. Drain and rinse before using.

In a large stock pot over medium heat, cook and stir onion and garlic in olive oil until onion becomes translucent, about 5 minutes. Pour in the chicken broth and 8 cups water, bring to a boil, and reduce heat to a simmer. Stir in soaked black-eyed peas, ham hocks, tomatoes, pepperoncini, bay leaf, garlic powder, thyme, and salt and pepper. Cover and simmer until peas are tender, ham meat is falling off the bones, and the broth is thickened, about 3 hours.