In a small bowl, whisk together the Dijon mustard, chili paste, soy sauce, rice vinegar, honey, sesame oil, and 1 teaspoon water until smooth and slightly pourable. Taste and adjust heat or sweetness as desired. Set aside at room temperature.

Peppers & Finish

Prep peppers

Rinse the shishito peppers and pat them dry thoroughly with paper towels. Dry peppers blister much better than wet ones. Leave stems intact for presentation.

Heat pan

Place a large cast-iron or heavy-bottom skillet over high heat. Heat until very hot, about 2–3 minutes. You want the pan smoking slightly but not burning oil.

Blister peppers

Add the neutral oil to the hot pan and swirl to coat. Add the dry shishito peppers in a single layer (they can overlap slightly). Let them sit, undisturbed, for 1–2 minutes to blister on one side, then use tongs to toss and turn occasionally, blistering all over. Total blistering time: 4–6 minutes, until skins are charred in spots and peppers are softened but still bright green.

Season

Remove the pan from heat and immediately transfer peppers to a serving bowl or platter. Sprinkle with the coarse sea salt and the toasted sesame seeds, tossing gently to distribute.

Serve with sauce

Serve the blistered shishitos hot with the chili mustard sauce on the side for dipping or drizzled lightly over the peppers. If using, sprinkle sliced scallions, drizzle a scant 1/4 teaspoon toasted sesame oil, and offer lemon wedges for brightness.