Season the salmon fillets with salt and pepper on both sides. Set aside.
In a large lidded skillet or saucepan, melt the ghee over medium heat. Add the garlic, ginger and chile, and cook for 2 to 3 minutes, stirring frequently, until golden brown and fragrant. Season with salt and pepper. Add the cumin seeds and toast for 15 seconds, then stir in the tomatoes, coriander and turmeric.
Stir in the coconut milk and season with salt to taste. Cook for 6 to 8 minutes, uncovered, until liquid is slightly reduced and the tomato skins are bursting.
Stir in the spinach and gently nestle the salmon fillets into the curry, submerging as much as possible. Cover and simmer over medium-low until salmon is cooked through, 4 to 7 minutes. Serve over rice and garnish with herbs.
