Rinse the fish in cold water and pat dry with paper towels. With a knife, cut a slit diagonally near the fin. Season the fish inside and out with salt.
Stuffed half of the chopped onion and tomato in one fish and the other half in the second fish.
Place each fish on a large sheet of aluminum foil. Carefully seal all edges of the foil to form enclosed packets.
Pour water into a wok or stockpot and set a steamer in the wok or on the rim of the stockpot. Make sure the water does not touch the bottom of the steamer. Bring the water to a boil over high heat.
Place the aluminum foil holding the fish in the steamer, cover, and steam for about 30 minutes.
While the fish is steaming, in a small bowl, stir together the soy sauce, lemon juice, and 1 chili. Set aside.
Remove the fish from the steamer and place it on a plate. Carefully open the top of the aluminum foil and serve. Bon Appetit!