Season salmon fillets with kosher salt. Line a baking sheet with foil and brush lightly with vegetable oil.

Preheat the oven's broiler to high and set the oven rack about 8 inches from heat source.

Process garlic, tarragon, and parsley in a blender or in a mortar and pestle to form a loose paste.

Mix mayonnaise, Dijon mustard, lemon juice, and cayenne pepper into garlic-herb mixture until combined.

Place salmon fillets, skin-side-down, on the baking sheet. Spread herb mixture over the top and sides of each fillet.

Cook under the preheated broiler until fillets are well-browned, about 5 minutes. Turn the broiler off and turn the oven to 350 degrees F (175 degrees C).

Bake until internal temperature of salmon is 130 degrees F (55 degrees C) and salmon flakes easily with a fork, about 3 to 4 minutes.