Step 1

Season fish generously with salt (but don’t go crazy). Let sit 20 minutes to absorb seasoning.

Step 2

Meanwhile, mix mushrooms, kombu, ginger, garlic, mirin, soy sauce, red pepper, and 2 cups water in a medium saucepan fitted with a steamer insert or bamboo steamer. Bring to a simmer over medium heat, discard kombu, and continue to simmer, adjusting heat as needed, until flavors meld, about 5 minutes.

Step 3

Rinse fish and pat dry. Scatter daikon across bottom of steamer insert and lay fish over. Steam fish, maintaining an active simmer in liquid (err on the side of less heat if you aren’t sure), until fish is just opaque at the center and a tester inserted into the thickest part of the fillets meets no resistance, 6–8 minutes.

Step 4

Transfer fish to a plate. Discard mushrooms, then carefully pour steaming liquid into a blender. Add spinach and jalapeño. Remove cap from hole in lid, cover opening with a kitchen towel, and start blender on lowest speed to prevent hot liquid from splashing out the top like a geyser. Gradually increase speed and blend until smooth.

Step 5

Divide fish, daikon, and broth among bowls. Top with cilantro.