1. Preheat oven to 350*F. Bake whole, unpeeled yams until very tender, about 1 hour, 20 min. Refrigerate until cold.

2. Peel yams and mash flesh in a large bowl until smooth. Pulse cauliflower and spinach in a food processor until finely chopped. Stir mixture into mashed yams, along with 1/2 cup Parmesan, 1 egg, 3/4 cup pano, salt, garlic powder, and cayenne, if desired.

3. Preheat oven to 450*F. Line 2 baking sheets with parchment paper. Beat remaining 3 eggs in a medium bowl. Toss remaining 1 1/2 cups of panko with remaining 1/2 cup Parmesan on a large, shallow plate or pie plate.

4. Using slightly dampened hands, form veggie mixture into 1-inch balls and flatten slightly into oblong nuggets. Place nuggets on a plate in single layer (you can transfer filled plates to refrigerator as you work). Gently dip one nugget at a time into egg, letting excess drip off, then dredge in panko mixture on both sides. Place finished nuggets on baking sheets.

5. Bake, flipping nuggets once, until golden brown, about 30 min.