Heat oil in a medium saucepan over medium-low heat
Add shallots, ginger, garlic, lemongrass, turmeric, salt, and water. Cover and cook until very tender, 8 to 10 minutes. Uncover and cook until the liquid evaporates, 1 minute.
Put the mixture into a food processor and puree to form a paste.
Season the salmon filets with salt and pepper.
Add 1 T oil to the pan and heat until hot but not smoking. Add the salmon and cook until lightly browned, 2 to 3 minutes. Remove the salmon and let it sit on a plate.
Add the squash and peppers and cook 2 to 3 minutes. Stir in the lemongrass paste and cook until fragrant, about 1 minute. Add the coconut milk, ¾ cup water. Boil, then simmer.
Nestle in the salmon, seared side up. Simmer, covered, until the fish is cooked through, 2 to 3 minutes.
Remove the pan from the heat. Stir in the cilantro, basil, lime juice, and lime zest.
Serve over cauliflower rice.