In a bowl combine the lemon zest, dill, parsley, chervil, and black pepper. Season the fish with 1 1/4 teaspoons of the salt, then lightly brush each piece with 1 teaspoon of the Dijon mustard on 1 side. Firmly press the mustard coated side of each of the drum fillets into the lemon-herb mixture. In a skillet, preferably nonstick, heat the vegetable oil. Place fillets, coated side down, into the hot oil. Cook for 3 to 3 1/2 minutes, or until the crust turns golden brown. Flip and continue to cook for 3 minutes longer or until the fish flakes easily. Meanwhile, in a separate pan, place the bok choy cut side down. Add a little water to the pan to steam the bok choy until just tender, about 7 minutes. Remove the bok choy from the pan into a bowl and toss with the olive oil and season with salt and pepper.

When ready to serve, divide the bok choy among 4 dinner plates and place 1 fish fillet over the top of each serving of bok choy. Drizzle with lemon juice and extra-virgin olive oil to taste.