Method

1. Position an oven rack in the top of the oven, and preheat to 170°C.

2. Put the sweet potatoes on a rimmed baking sheet, and bake until fork-tender, 40 to 50 minutes. Let cool completely. (The potatoes can be baked, cooled and refrigerated a day ahead.) Split each in half lengthwise, and scoop out most of the flesh, leaving about a 1/4-inch border all around. (Save the scooped-out flesh for making mashed sweet potatoes later.)

3. Preheat the oven to 200°C. Put a rack on a rimmed baking sheet. Arrange the potato skins skin-side up on the rack, and brush with 2 tablespoons of the oil.

4. Bake until the skins are slightly browned, 20 to 30 minutes.

5. Let cool completely, then cut each in half crosswise. Arrange the pieces skin-side down on the rack, and sprinkle each with mozzarella, Parmesan and scallions.

6. Bake until the mozzarella melts, 8 to 10 minutes.

7. Remove the potato skins from the oven, and drizzle with the remaining tablespoon of oil. Top each with some salsa verde and avocado.

8. Sprinkle with crushed chips.