Peel the sweet potatoes and cut them into 1.5 cm cubes. Dice the onion and bell pepper, mince the garlic and chipotles, drain and rinse the beans, and mix the cumin, paprika and oregano in a small bowl.
Heat 1 tbsp of the oil in a 30 cm / 12-inch cast-iron skillet over medium-high heat for 2 minutes. Add the sweet potatoes in one layer with 1/4 tsp of the salt and cook for 8 minutes, stirring every 2 minutes, until the edges are browned and the centers are still firm. Move them to a plate.
Add the remaining 1/2 tbsp oil and lower the heat to medium. Cook the onion and bell pepper for 3 minutes until softened, then add the turkey. Break it up and cook for 7 to 8 minutes until no pink remains and it reads 165 F / 74 C.
Stir in the garlic, chipotles, adobo sauce, tomato paste, spice mix and the remaining 1/2 tsp salt. Cook for 1 minute until fragrant and the paste darkens, then pour in the water and scrape up the browned bits.
Return the sweet potatoes to the skillet and stir to coat. Cover, lower the heat to medium-low and cook for 10 minutes, stirring once, until a fork slides into a cube with no resistance. If the pan looks dry, add 2 tbsp of water.
Stir in the black beans and lime juice and cook uncovered for 2 minutes. Sprinkle the cheese on top, cover and cook for 2 minutes until melted. Serve with 2 tbsp Greek yogurt per plate and cilantro.