Green Curry Lentil Soup

Name: Green Curry Lentil Soup
Cuisine: Thai
Ingredients: 2 Tbsp. virgin coconut oil; 1 small onion, chopped; 2 garlic cloves, finely chopped; 1 1" piece peeled ginger, finely chopped; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; ¼ cup Thai green curry paste; 1 medium sweet potato, peeled, cut into ½" cubes; ¾ cup brown or green lentils; 4 cups low-sodium chicken or vegetable broth; 1 13.5-oz. can unsweetened coconut milk, shaken well; 4 cups (loosely packed) baby spinach leaves; ½ tsp. (or more) fish sauce; Small handful cilantro leaves with tender stems and lime wedges (for serving)