In a large, heavy-bottomed Dutch oven, warm the olive oil over medium heat.
Add the chopped celery, carrot, onion, and salt.
Sauté for about 5 minutes, until the onions soften and become translucent.
Stir in the dried thyme, oregano, cumin, chipotle chili, and bay leaves. Toast the spices for 2 minutes until fragrant, awakening their flavors.
Pour in the washed black-eyed peas and the vegetable stock. Increase the heat to bring the soup to a boil, then reduce to a gentle simmer.
Cover and cook for 2 hours, or until the beans are completely tender.
Check occasionally and add more stock or water if the liquid level gets too low.
Add the diced sweet potatoes to the pot and continue to simmer for another 20 minutes.
Stir in the chopped mustard greens and diced tomatoes.
Cook for a final 10 minutes, until the sweet potatoes are fork-tender and the greens are heated through.
Remove the chipotle chili halves and bay leaves.
Taste and adjust the seasoning with more salt and pepper if needed. If the soup is too thick, thin it with a splash of vegetable stock or water to reach a brothy consistency.
Ladle the hot soup into bowls and serve immediately, garnished with a generous handful of cornbread croutons and a sprinkle of fresh cilantro.
Don't have mustard greens? Kale, spinach, or collard greens make excellent substitutes.
Add tender greens like spinach in the last 2-3 minutes of cooking.
