Step 1

Place a rack in upper third of oven and preheat to 400°. Line a rimmed baking sheet with foil. Line up 1½ lb. asparagus on a cutting board and trim woody ends (about bottom 2") with a chef’s knife; discard. Slice spears into 1" lengths and transfer to prepared baking sheet. Drizzle with 2 tsp. avocado or vegetable oil and season with kosher salt. Using your hands, toss well to coat. Push asparagus to one side of baking sheet.

Step 2

Pat four 4–6-oz. skin-on arctic char, sea bass, or salmon fillets dry with paper towels. Place, skin side down, on empty half of baking sheet.

Step 3

Now, make the miso butter: Place 3 Tbsp. unsalted butter in a small microwave-safe bowl. Microwave on medium power in 20-second intervals until melted. (Alternatively, melt butter in a small skillet over medium.) Add 6 Tbsp. white or yellow miso, 1 Tbsp. plus 1½ tsp. Sriracha, and 1 Tbsp. sugar. Smash and peel 9 garlic cloves. Finely grate on a Microplane into miso butter. Peel one 3" piece ginger with a spoon; finely grate into butter. Stir to combine.

Step 4

Melt remaining 2 Tbsp. unsalted butter in another microwave-safe bowl. Stir in ⅔ cup panko.

Step 5

Dollop about two-thirds of miso butter over fish, spreading it into an even layer with spoon. Sprinkle buttered panko over fillets and gently press with your hands to adhere. Roast fish and asparagus until fillets are firm when sides are gently pressed, 15–17 minutes.

Step 6

Heat broiler (to low, if your oven allows). Broil (watching carefully), rotating baking sheet halfway through for even browning, until panko is golden brown, about 3 minutes. Remove baking sheet from oven and immediately drizzle remaining miso butter over asparagus; toss to combine.

Step 7

Slide a fish spatula between fish skin and flesh and do your best to gently lift away the fillets (skin won’t be crispy, so it’s best left behind). Serve fish with asparagus.