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