line a baking sheet with the banana leaves and preheat the oven to 400 F. Cut 2 widthwise slits across both sides of each fish. Liberally coat both sides with salt. Warm 1 1/2 Tbsp of the oil in each of two large skillet over medium-high heat. Sear the fish until the skin is lightly browned and crisp, about 2 minutes on each side. Tip the fish, along with the oil it was cooked in, into the other pan
In the empty pan, combine the shallots, garlic, lemongrass, bay leaves, chilies, cinnamon, cardamon, peppercorns, coriander seeds, and coffee beans. Stir over medium-high heat until the shallots and garlic are lightly browned and the mixture is aromatic, about 3 minutes
Spread the spice mixture over the banana leaves on the baking pan and lay the fish on top. Roast, turning the pan halfway through cooking, until the fish is cooked through and soft to the touch, about 25 minutes. Transfer the fish to a serving plate and tent with foil while you make the sauce
Transfer the coffee bean and spice mixture from the baking sheet to a large saucepan and place over medium-high heat. Add the coconut milk and simmer for 3 minutes. Turn off the heat. Add the fish sauce and lime juice, and let steep for a minute. Taste and add more fish sauce or lime juice if needed. Strain and serve over the fish. Garnish with a few of the shallots, garlic cloves, and coffee beans