Preheat oven to 375 degrees and lightly coat a 9x13” baking dish with 1 tablespoon of the ghee.
Season salmon with salt and pepper to taste, thyme, and then top with mustard in an even layer.
Place the salmon in the baking dish. In a separate medium bowl, add ghee, broccolini, onions, garlic, and toss to combine.
Surround fish with veggie mixture and bake 15-20 minutes, until fish is opaque and cooked through. Serve hot with lemon squeezed over the top.