Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Quarter lemon. Dice potatoes into ¼-inch pieces.

In a small bowl, combine mayonnaise, a squeeze of lemon juice (big squeeze for 4), salt, and pepper. Set aside until ready to serve.

In large oven-ready tray, toss potatoes with a drizzle of olive oil, salt, and pepper. (For 4 servings, divide between two large trays, using a drizzle of olive oil in each tray.) 

Roast on top rack (be sure your oven has preheated!), tossing halfway through, until browned and cooked through, 20-25 minutes. (For 4, bake two trays side by side on top rack.)

Reserve half the pesto in a second small bowl for serving.

Once potatoes have roasted 12 minutes, pat salmon* dry with paper towels. Season all over with salt and pepper; place salmon, skin sides down, in small oven-ready tray. Spread tops of salmon with a thin layer of remaining pesto. (For 4 servings, divide everything between two small trays.)

Roast salmon on top rack (side by side with potatoes) until cooked through, 8-10 minutes. (For 4, transfer trays with potatoes to middle rack; roast two salmon trays side by side on top rack.)