Preheat oven to 400° F.
Combine olive oil, lemon juice and zest, fresh herbs, Dijon mustard, kosher salt, and black pepper in a shallow baking dish.
Place trout fillet in the oil and herb mixture, spooning the marinade over the fish until covered.
Bake the trout, uncovered, until the flesh is just cooked enough for it to fall apart with the touch of a fork—about 10-14 minutes depending on the thickness of the fish. Remove the trout just before it's completely cooked through, cover loosely with foil, and let sit for 5 minutes.
Remove trout from baking dish, drizzle with extra marinade, and serve hot.