01 - Preheat the oven to 425°F. Line a large baking sheet with parchment paper or foil for easy cleanup.
02 - In a large bowl, toss the halved baby potatoes and red onion with 2 tablespoons olive oil, half of the lemon zest, 0.5 teaspoon salt, and 0.25 teaspoon black pepper. Spread evenly on the prepared baking sheet.
03 - Roast the potatoes and onions for 15 minutes until beginning to soften.
04 - Meanwhile, in a small bowl, combine remaining olive oil, lemon juice, remaining lemon zest, garlic, parsley, dill, thyme, 0.25 teaspoon salt, and 0.25 teaspoon black pepper.
05 - Remove the baking sheet from the oven. Nestle the salmon fillets among the potatoes and onions. Brush each fillet generously with the lemon-herb mixture and top with lemon slices.
06 - Return to the oven and roast for an additional 10-12 minutes, or until the salmon is just cooked through and the potatoes are golden and tender.
07 - Serve immediately, garnished with extra fresh herbs and lemon wedges if desired.