Line a 1/2 sheetpan with parchment paper.
Add the diced potatoes and carrots, the sliced onions, diced jalapeño and tomatoes. Pour some of the vinaigrette over the veggies. Mix to coat.Note: I used 1/4 plus 1 tablespoon of the vinaigrette. Use enough to thoroughly coat the veggies. Use a 1/4 of the remaining salt and pepper mixture to sprinkle on the veggies. Add the remaining crushed garlic, oregano and the chopped rosemary. Mix.
Cut two scores on each fish - see instruction video.
Season the fish with all of the remaining salt and pepper mixture.
Place the fish, cut side up, on top of the veggies. Drizzle up to 1 tablespoon vinaigrette all over each of the fish. Rub to coat the fish all over.
Use some of the sliced onions to stuff inside the fish cavities - don't over stuff. Add 2 to 3 slices of the lemon inside each fish cavity.
Add the grated Parmesan and ground pistachio nuts to a bowl. Mix to combine.
Spinkle about 1/2 of the cheese/nut mixture on top of the fish and add a little bit inside the cavity. Use the remaining mixture to sprinkle all over the veggies. Drizzle 1/2 to 1 tablespoon of the vinaigrette over the topping.
Bake the fish for 30 to 35 minutes until it comes out flakey.Note: The internal temperature should reach 170 degree doneness. Plate and serve the fish with the veggies. OPTIONAL: drizzle up to 1 tablespoon of the vinaigrette over the cooked fish. Enjoy.