This is a Martha Stewart recipe and it's pretty tasty. I often buy bags of frozen cod at Costco. Cod is pretty mild so I try to find ways to jazz it up a bit. Good served with brown rice.
2 medium leeks, white and light-green parts only, thinly sliced, rinsed well, and patted dry
2 tablespoons fresh lemon juice
1 tablespoon olive oil
1 teaspoon freshly grated lemon zest
3 sprigs thyme, or 1 teaspoon dried thyme
Salt and fresh ground pepper
1 can diced tomatoes
2 cod fillets 3/4 to 1 inch thick
Preheat oven to 450 degrees. In a 9-by-13-inch baking dish, toss together leeks, lemon juice, oil, lemon zest, thyme, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Cover with foil, and bake until leeks just begin to soften, 8 to 10 minutes.
Remove baking dish from oven. Add tomatoes, and toss to combine. Season both sides of cod fillets with 1/2 teaspoon salt and 1/4 teaspoon pepper; place on top of vegetables.
Cover dish and bake until fish is opaque throughout, about 15 to 20 minutes. Serve immediately.