Spiced Sweet Potato Sandwich With Feta

Name: Spiced Sweet Potato Sandwich With Feta
Ingredients: 1 large sweet potato (about 12 oz.), peeled, sliced lengthwise into ¼–½-thick planks; 1 tsp. ancho chile powder; ½ tsp. ground cumin; 3 Tbsp. extra-virgin olive oil, plus more for drizzling; Kosher salt, freshly ground pepper; 1 medium beet, peeled, cut into thin matchsticks or grated on the large holes of a box grater; ½ small red onion, thinly sliced; 3 Tbsp. seasoned rice vinegar; ½ cup mayonnaise; 1 large garlic clove, finely grated; 1 Tbsp. plus 1 tsp. fresh lemon juice; 2 sesame kaiser rolls, split; 1½ cups parsley, mint, and/or cilantro leaves; 5 oz. block feta, thinly sliced into planks, divided