Make the creamed spinach and mushrooms. In the same skillet on the grill, add additional oil if needed. Add the mushrooms, close the lid and cook until lightly browned and begin to soften, stirring after 5 minutes, 7-8 minutes.
Add the shallots and garlic and stir to combine. Close the lid and cook until fragrant and the shallots have softened, 2-3 minutes.
Stir in the Dijon mustard, broth, cream, and mascarpone cheese. Close the lid and cook until the sauce has thickened slightly, 3-4 minutes.
Stir in the Parmesan and spinach. Close the lid and cook until the spinach has wilted, 3-4 minutes.
Season the creamed spinach and mushrooms with smoked sea salt and pepper, as desired. Add the salmon filets to the pan, skin-side-down, nestled in the spinach and mushrooms. Close the lid and cook until the salmon reaches an internal temperature of 130°F, or desired doneness.
Remove the salmon, and creamed spinach and mushrooms from the grill. Garnish with fresh herbs, and serve warm. Enjoy!