Mix mustard, mayonnaise, Italian dressing, ranch dressing, and garlic powder together in a bowl. Squeeze 1/2 lemon over the mixture. Slice remaining lemon halves.
Place salmon fillet on a large sheet of aluminum foil. Coat with mustard mixture and top with lemon slices. Cover with mint leaves, rosemary sprig, chives, dill sprig, and garlic, in that order. Wrap in aluminum foil and refrigerate for at least 1 hour.
Preheat the oven to 450 degrees F (230 degrees C). Place wrapped salmon on a baking sheet.
Bake in the preheated oven until flesh flakes easily with a fork, 30 to 45 minutes. Unwrap carefully and discard herb sprigs before serving.