In this simple and flavor-packed sheet-pan dinner, white fish is topped with a lemon-dill-mustard dressing for a bright, herby flavor that pairs well with juicy tomatoes and crunchy green beans. Serve it directly from the pan, pouring the remaining dressing on the green beans and tomatoes. Most of this dish is hands-off, meaning you'll have a lot of downtime while the beans and tomatoes cook, so you can use that time to zest the lemon, season the fish, make the dill dressing, clean up and set the table.
Technique tip: If you use a leaner and thinner fillet of fish than hake or cod, then you will need to reduce the cooking time by at least 4-5 minutes, adding it to the sheet pan about 20 minutes after the cooking process. If you'd like to blister the tomatoes or green beans more, then turn on the broiler during the last 3 minutes of the cooking process and finish the fish underneath it.
Swap option: If you're not a fan of dill, swap it for mint, cilantro or parsley.
Heat the oven to 400 F.2.
On a sheet pan, season the green beans and tomatoes with 2 tablespoons olive oil, salt, pepper and 1/2 teaspoon red pepper flakes. Cook for 15 minutes.3.
Meanwhile, coat the fish with 1 tablespoon oil and season well with salt, pepper, 1/4 teaspoon red pepper flakes and half the lemon zest. Remove the sheet pan from the oven, push the green beans and tomatoes to the sides so you can place the fish skin-side down, if any, in the center of the pan. Rub the cut side of one of the lemon halves in the pan juices, and place cut-side up in the corner. Cook until the fish easily flakes and a fork pierced into the thickest part doesn't meet a rubbery resistance, about 15 minutes.4.
While the fish cooks, in a small mixing bowl, combine the remaining lemon zest, juice of 1 lemon, mustard and dill, and whisk in the olive oil until smooth. Season to taste with salt and pepper.5.
Squeeze the cut lemon half over the sheet pan, then spoon some of the dressing over the fish, serving the remaining on the side. Garnish with dill, cut the remaining lemon into wedges and serve with the fish.