Season the top side only of the fish fillets with kosher salt and fresh pepper.
Heat a wide sauté pan over medium high heat; when hot add the 2 tablespoons of oil to coat the pan. When the oil is hot place the fish fillets, salted side down, into the hot oil. Leave the fish untouched to sauté for 2 to 3 minutes. When you see the edges of the fish start to turn crispy brown you can then gently turn each piece of fish over using a fish spatula or other wide set perforated spatula. Once the fish is turned leave untouched to sauté for another minute or 2 until the fish is just cooked through. Remove the fish from the pan and transfer to your serving plates. Keep the sauté pan with all the accumulated fond, which is the brown stuff stuck to the bottom of the pan, over medium high heat.
Add the onion to the pan and sauté until the onion turned golden brown.
Stir in the garlic and sauté briefly until fragrant for about 30 seconds.
Pour the wine (or stock) into the hot pan to deglaze; this means the shock of the liquid to the hot pan will cause the brown fond to release from the bottom of the pan.
Stir the tomatoes into the pan and bring the sauce to a simmer.
Remove the pan from the heat and season the sauce with a generous pinch of sea salt and fresh pepper.
Stir in the fresh herbs and spoon the sauce over each piece of fish.