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