01 - Preheat oven to 425°F. Line a large rimmed baking sheet with parchment paper or foil for easy cleanup.
02 - In a small bowl, whisk together olive oil, lemon juice, minced garlic, Dijon mustard, honey, salt, black pepper, smoked paprika, and crushed red pepper flakes.
03 - Spread green beans and sliced red onion evenly on the prepared baking sheet. Drizzle with half the marinade and toss to coat.
04 - Nestle salmon fillets among the vegetables. Brush the tops of the salmon with the remaining marinade. Arrange lemon slices over salmon and green beans.
05 - Roast in the preheated oven for 15 to 18 minutes, until salmon is cooked through and green beans are tender-crisp.
06 - Remove from oven, sprinkle with chopped parsley, and serve immediately.