Place the sweet potatoes and bell pepper on a baking sheet. Drizzle with olive oil and season with salt and pepper. Roast until softened and slightly browned, about 20 minutes.
Place rice in a small pot. Add 2 cups water and a pinch of salt. Cover and simmer until the water is absorbed and the rice is cooked, about 20 minutes.
In a small bowl mix the lime juice, grapeseed oil and cumin together until incorporated.
In a large bowl, combine the rice, sweet potatoes, bell pepper, chicken, corn and black beans. Pour the cumin vinaigrette and cilantro, and mix gently until well combined. Portion on individual serving plates and serve.