My cherry tomatoes are going to start ripening next week, so I am looking forward to making this. Martha suggests using a ceramic baking dish to avoid interaction between aluminum pans and the tomatoes. From Martha Stewart Living.
Preheat oven to 425 deg F. Toss together the potatoes, tomatoes, garlic, oregano, 1 tbl oil and 1/2 tsp salt. Season with salt.
Layer the potatoes in a 9x13 pan, overlapping as necessary and top them with the tomatoes. Roast until tomatoes are juicy and potatoes are tender, about 25 minutes. Remove from oven.
Rub fish with the remaining 1 tsp oil. Season with the remaining 1/2 tsp salt and tuck 3 slices lemon into each cavity. Move tomatoes towards the side of pan and arrange the trout on top of the potatoes.
Roast until the fish is done, about 20 minutes. Serve immediately.