Heat olive oil in a Dutch oven or large stock pot over medium-high heat. Add onion, celery, carrots, and poblano. Sauté 5-7 minutes, until softened and golden, stirring occasionally. Add garlic, cook 1 minute, stirring frequently. Add the sherry, let simmer and reduce by half, about 5 minutes.
Stir in beans, broth, bay leaves, and cumin. Bring to boil, add sweet potatoes and rosemary, reduce to simmer. Cover with tilted lid and simmer 15 minutes or until sweet potatoes are fork tender. Remove bay leaves.
Add swiss chard by the handful letting each addition wilt into the stew. Remove from heat once greens have softened. (Can be made 1 day ahead. Let cool, cover and chill. Rewarm over medium heat.) When ready to serve, add lime juice and oregano. Season with salt and pepper to taste. Garnish with green onion and cheese crumbles, if desired.
If you're not sticking to a vegetarian diet, 8 ounces of cooked ham, sausage, prosciutto, or bacon would go very well in this stew and easily served on the side.