Season the salmon with salt and pepper.
Heat oil in a large skillet over medium heat. Add the salmon and sear until lightly browned, about 1½ minutes per side. Transfer to a plate.
Reduce heat to medium. Add the shallot and cook until softened, about 1 minute. Stir in garlic and ginger and cook until fragrant, about 30 seconds.
Add coconut milk, lime juice, salt, and cumin. Bring to a gentle simmer.
Whisk the tapioca flour with water, then stir into the sauce. Simmer until slightly thickened, about 3 minutes. Taste and adjust seasoning.
Return the salmon to the skillet. Reduce heat to medium-low and simmer until just cooked through, 8 to 10 minutes. Finish with lime zest and cilantro.