If you haven't yet, take the corn out of the freezer and allow it to begin thawing. Preheat the oven to 400ºF.
Peel the sweet potatoes, then cut them into a small dice (1/4-1/2 inch cubes). Place the cubes on a baking sheet, drizzle with cooking oil, cumin, and a pinch or two of salt. Toss the sweet potato cubes until they are all coated in oil and spices. Roast the sweet potatoes for about 30 minutes, or until they are soft and slightly browned on the edges. Remove from the oven and let cool slightly.
While the sweet potatoes are roasting, prepare the lime crema. Use a small-holed cheese grater or a zester to remove the thin layer of green zest from the lime. Add about 1 tsp of the zest and 1 Tbsp of the lime juice to the sour cream, along with the minced clove of garlic and 1/4 tsp of salt. Stir to combine. Taste and adjust the lime juice as desired. Refrigerate the crema until ready to use.
Heat a large skillet over medium to medium-high heat. Once hot, add 2 Tbsp cooking oil and swirl to coat the surface of the skillet. Add the thawed corn and let cook until the corn is blistered and charred on the edges. Avoid stirring too often to allow it to blacken a bit. Let the corn cool slightly.
Finely dice the red bell pepper and red onion. Rinse and drain the black beans. Pull the cilantro leaves from their stems and then roughly chop.
Combine the roasted sweet potatoes, blackened corn, black beans, red bell pepper, red onion, and cilantro in a large dish. Stir to combine. Add some of the lime crema and toss until the salad is lightly coated. Add a little more lime crema on top just before serving.