Add diced tomatoes, onions, herbs (if you aren't using herbed diced tomatoes add some basil and oregano- about 2 tsp each), and capers and mix.
Add fish to pan, toss a bit of the rustic sauce mix over the fish.
Pop in oven and bake about 10-15 minutes- until fish is flaky and white. This cooking time depends on the size of your filets and your oven- check after 8 minutes, and then again after 12.