Leftover fish and vegetables from tonight are the perfect starting point for Asian-Style Salmon Burgers later in the week.
Preheat oven to 450 degrees, with racks in middle and lower thirds. On a rimmed baking sheet, toss carrots and onions with oil and season with salt and pepper. Roast on middle rack until tender and onions are golden, about 20 minutes, stirring halfway through. Line another rimmed baking sheet with parchment. Season salmon with salt and pepper and roast on bottom rack until opaque throughout, about 12 minutes.
Meanwhile, in a large pot of boiling salted water, cook orzo according to package instructions. Drain, return to pot, and toss with butter, dill, parsley, and lemon juice. Season with salt and pepper. Transfer 4 salmon fillets and 1 cup vegetables to an airtight container; refrigerate, up to 3 days. Serve remaining salmon fillets and vegetables with herbed orzo.