Steamed Rockfish with Thai Citrus

Name: Steamed Rockfish with Thai Citrus
Ingredients: 1 medium shallot; 5 fresh green peppercorns; 2 garlic cloves, peeled; 1 (2-inch) piece fresh ginger, peeled; 1 (2-inch) piece fresh turmeric, peeled; 1/2 lemongrass bulb, cut into thin rounds (about 1 tablespoon); 3 makrut lime leaves, thinly sliced; 1 tablespoon kosher salt; 1/2 teaspoon palm sugar or granulated sugar; 3 tablespoons plus 1 teaspoon coconut oil, divided; 2 medium-size sour oranges, juiced (about 1/2 cup juice) (see Note); 3 (8-ounce) bunches fresh spinach, washed, stems removed; 2 (1 1/2- to 2-pound) whole fish (such as rockfish), cleaned and scaled; Cooked jasmine rice, for serving