Heat oven to 180°C. Season the trout cavity with salt and pepper and drizzle with 1 tbsp oil. Lay the lemon slices inside across the cavity of the fish. Stuff with half the thyme and parsley.
Using kitchen string, firmly tie the trout crosswise about 4 times, spacing evenly along the fish, tying and knotting loose ends
Pick leaves from remaining thyme and parsley and chop. Mix herbs with remaining oil and some seasoning. Rub mixture over the outside of the fish, and then transfer to a roasting tray lined with baking paper.
Bake trout for about 35-40 minutes. Remove from the oven, cover with foil and rest for about 10 minutes. Serve whole at the table.