Season salmon with salt and pepper.

Heat 1/3 cup oil in a 12-inch stainless steel skillet over medium-high heat until shimmering.

Add salmon, skin-side down, and immediately reduce heat to medium-low.

Cook, pressing down gently with a spatula to ensure contact, until skin is rendered and crisp, about 6 minutes.

Flip salmon and cook until an instant-read thermometer inserted into the thickest part registers 120°F (49°C) for medium rare or 130°F (54°C) for medium, about 1 minute longer.

Transfer salmon to a paper towel-lined plate and allow to cool.

Once cooled, flake salmon using your hands; discard skin.

Wipe out skillet.

Add remaining 2 tablespoons oil and heat over medium-high heat until shimmering.

Add shallot and a pinch of salt and cook until softened, about 2 minutes.

Add couscous and cook, stirring, until lightly toasted and fragrant, about 1 minute.

Add broth, stirring to combine, and adjust heat to maintain a simmer.

Cook until most of the liquid has been absorbed and couscous is tender.

Strain any excess liquid.

In a large serving bowl, mix together mustard and lemon juice.

Stir in couscous, along with dill and spinach, stirring to fluff the couscous and wilt the spinach.

Stir in flaked salmon and season with salt and pepper.

Garnish with dill and serve right away.