Heat oil in a large cast-iron skillet over medium-high heat. Add sweet potatoes and ¼ teaspoon salt. Cook, stirring occasionally, until beginning to brown, 5 to 7 minutes. Transfer the pan to the oven and bake until the sweet potatoes are soft, 15 to 20 minutes.
Meanwhile, combine sour cream, lime juice and the remaining pinch of salt in a small bowl.
Top the sweet potatoes with corn, cheese and beans. Continue baking until the cheese is melted, about 5 minutes. Top with tomatoes, scallions and avocado. Drizzle with the sour cream mixture. Serve topped with cilantro (if using).
Serving size: about ½ cup each
Per serving: 174 calories;8 g fat(2 g sat); 5 g fiber; 22 g carbohydrates; 4 g protein; 40 mcg folate; 7 mg cholesterol; 5 g sugars; 0 g added sugars; 11,478 IU vitamin A; 7 mg vitamin C; 74 mg calcium; 1 mg iron; 166 mg sodium; 460 mg potassium