Keep the serving plates in the oven at the lowest setting so they are warm when you serve.
Heat the oil in a skillet, over medium-low heat. Add the onion and garlic and sauté gently, with occasional stirring, until softened, about 5 min. Add the spices and grated ginger, then cook 2 min with stirring. Add the strained tomatoes, broth and half of the lemon juice. Season with salt and pepper to taste, cover and continue to cook 5 min.
Add the fish fillets, cover and cook 5 min on one side. Turn the fillets then cook 5 min on the other side, or until the fish turns opaque.
Adjust the seasoning, adding the remaining lemon juice Spoon the sauce over the fish, sprinkle with optional cilantro, then serve on the warmed plates.