Preheat the oven to 200°C (400°F) and line a large rimmed baking sheet with parchment paper.
In a small mixing bowl, whisk together the olive oil, lemon juice, minced garlic, smoked paprika, oregano, cumin, salt, and black pepper to create the marinade.
Arrange the salmon fillets, shrimp, asparagus, and bell pepper strips on the prepared baking sheet in a single layer.
Drizzle the marinade evenly over the seafood and vegetables, then use tongs or clean hands to toss gently until everything is well-coated.
Place the lemon slices over the salmon fillets and interspersed among the shrimp.
Roast in the center of the oven for 12 to 15 minutes, or until the salmon reaches an internal temperature of 63°C (145°F) and the shrimp are opaque and pink.
Remove from the oven and garnish immediately with fresh chopped parsley before serving.