Trim the stem ends of the king oyster mushrooms. Holding each mushroom lengthwise, slice into 6–8mm (1/4 inch) thick rounds. For an oyster-like shape, slice at a slight angle so each piece has a broad, fan-shaped edge.

Using a paring knife, gently score the flat side of each slice in a shallow crisscross pattern (this helps texture and crisping). Pat the slices dry with paper towels to remove excess moisture.

Place the mushroom slices in a shallow bowl and drizzle with 1 tsp soy sauce; toss to coat evenly. Let sit 5–10 minutes to absorb flavor, then pat dry again.

Batter and Coating

Make umami flour mix

In a medium bowl whisk together the all-purpose flour, cornstarch, garlic powder, onion powder, smoked paprika, salt, and black pepper. Crumble the nori sheets into the dry mix and stir to combine.

Prepare wet batter

In a separate bowl whisk the aquafaba (or soy milk) with the cold sparkling water and 1 tsp soy sauce until slightly frothy. Gradually whisk 3 tbsp of the dry flour mixture into the wet liquid until a smooth, slightly thick batter forms. The batter should coat the back of a spoon; if too thick add up to 1 tbsp more sparkling water.

Panko mix

Place the panko breadcrumbs in a shallow dish and stir in the sesame seeds (if using) and a pinch of salt. Reserve for dredging.

Breading and Frying

Preheat oil

Pour vegetable oil into a deep skillet or medium saucepan to a depth of about 1–1.5 inches (approx. 3–4 cm). Heat over medium-high until oil reaches 175°C (350°F) or a small piece of batter sizzles and browns in about 30 seconds.

Working in batches to avoid crowding, dredge each mushroom slice first in the remaining dry flour mixture (shake off excess), then dip into the wet batter to coat completely, letting excess drip off, and finally press into the panko to coat both sides. Place coated pieces on a wire rack while you finish the rest.

Carefully lower a few slices into the hot oil without overcrowding. Fry 2–3 minutes per side, turning once, until golden brown and crisp. Use a slotted spoon or tongs to transfer to a paper-towel-lined tray to drain. Repeat with remaining slices. Keep finished pieces warm in a 90°C (200°F) oven if desired while you fry all batches.

Taste one and adjust seasoning with a sprinkle of salt if needed immediately after frying.

Sauce and Serve

Make quick sauce

In a small bowl combine the vegan mayonnaise, lemon juice, hot sauce (if using), and chopped dill or chives. Stir until smooth; taste and adjust salt, lemon or hot sauce to preference.

Arrange microgreens or shredded cabbage on a serving platter. Place the crispy vegan oysters on top, serve with lemon wedges and the quick sauce on the side for dipping. Garnish with extra chopped herbs and a sprinkle of crumbled nori or sesame if desired.

Serve immediately while hot and crispy.