Heat a large non-stick skillet over medium-high heat. Add oil to the pan and swirl to coat. Add turkey and ½ cup green onions; cook until turkey is mostly done, stirring to crumble, about 4 minutes. Stir in riced cauliflower, cumin, chili powder, garlic and smoked paprika; cook until cauliflower is tender, 3–4 minutes. Stir in tomato sauce and salt, cooking until thickened, 1–2 minutes.
Spoon turkey mixture into a 2-quart casserole dish coated with cooking spray. Top evenly with black beans and corn. Sprinkle cheese over the casserole. Bake until cheese melts and the casserole is bubbly around the edges, about 15 minutes.
Meanwhile, combine the remaining ½ cup green onions, tomatoes, cilantro and lime juice. Spoon the tomato mixture over the casserole just before serving.