Indian Fish Curry

Name: Indian Fish Curry
Ingredients: 1 Tbs. canola oil or clarified unsalted butter; 1 yellow onion, halved and thinly sliced; 2 garlic cloves, minced; 1 Tbs. minced ginger; 1 Tbs. curry powder; 1 can (14 oz.) coconut milk, well shaken; 2 small jalapeño or serrano chilies, halved and seeded; 1 1/2 tsp. salt, plus more, to taste; 1 lb. rockfish, snapper, cod or other white-fleshed fish fillets, pin bones removed and fillets cut into bite-size pieces; 1/4 tsp. ground turmeric; 2 plum tomatoes, seeded and chopped; Juice of 1 lemon; 1/2 cup hot water