Green Curry Coconut Cod

Name: Green Curry Coconut Cod
Ingredients: 1 Tbsp. vegetable oil; 1 shallot, coarsely chopped; 1 1 piece ginger, peeled, coarsely chopped; 2 (heaping) Tbsp. green curry paste (preferably Maesri); 1 13.5-oz. can unsweetened coconut milk; 5 oz. baby spinach; 1 tsp. dark or light brown sugar; ¼ tsp. Diamond Crystal or Morton kosher salt, plus more; 4 5–6 oz. skinless cod fillets, patted dry; Freshly ground pepper; 1 Tbsp. fish sauce; 1 lime; Steamed rice (for serving); 1 red chile (such as Thai or Fresno), thinly sliced; Cilantro leaves with tender stems (for serving)