Preheat grill to high.
Toss peas with oil and 1/4 teaspoon salt in a large bowl. Transfer to a grill basket. Grill, stirring occasionally, until charred, about 4 minutes.
Combine butter, miso, chile-garlic sauce (or Sriracha), vinegar and the remaining 1/4 teaspoon salt in the bowl. Add the peas and toss to coat. Garnish with sesame seeds and scallions, if desired.