Silky Pork and Cumin Stew

Name: Silky Pork and Cumin Stew
Ingredients: 1/2 small head of red cabbage, very thinly sliced; 2 Tbsp. apple cider vinegar; 1 tsp. sugar; Kosher salt, freshly ground pepper; 2 ripe avocados, unpeeled, halved, pits removed; 1/2 lime; Kosher salt; Chili powder (for serving); 1 (5-lb.) piece skinless, bone-in pork shoulder (Boston butt), patted dry; 3 Tbsp. extra-virgin olive oil; 3 medium onions, cut into 1-thick wedges; 2 heads of garlic, halved crosswise; 1/2 cup fine-grind cornmeal; 4 dried chiles de árbol; 2 tsp. cumin seeds; 3 Tbsp. apple cider vinegar; Crushed corn nuts, chicharrones, hot sauce, and/or sour cream (for serving; optional)