Step 1

In a food processor, combine the butter with the miso, lemon zest and lemon juice and puree until smooth. Add the 1 tablespoon of scallion and pulse just until incorporated. Scrape the miso butter into a large bowl and set aside.

Step 2

In another large bowl, toss the shrimp with the oil, garlic, chile powder and salt and let stand for 10 minutes.

Step 3

Light a grill or preheat a grill pan. Grill the shrimp over high heat, turning once, until just cooked through, about 4 minutes. Immediately add the shrimp to the miso butter and toss until well coated. Garnish the shrimp with scallions and the pickled mustard seeds and brine and serve.