1. Heat oil in a large cast-iron skillet over medium-high heat. Add onions and saute until brown (3-5 minutes).
2. Add sweet potato and cook, stirring, until it starts to brown (5-7 minutes).
3. Stir in garlic, jalapeño, cumin, and salt; saute until fragrant (30 seconds). Add water and cook, scraping up any browned bits, until liquid is absorbed (3-5 minutes).
4. Stir in corn and black beans. Cook until heated through. Stir in cilantro and season with pepper. Serve with lime wedges.