Preheat the oven to 425°F and line a large baking sheet with parchment paper.
Toss the cauliflower with 2 tablespoons of olive oil, paprika, and ¼ teaspoon salt. Spread evenly on the baking sheet and roast for 10 minutes.
While the cauliflower roasts, toss the green beans with the remaining tablespoon of olive oil and a pinch of salt. Pat the salmon dry and coat both sides with Cajun seasoning.
After the cauliflower has roasted for 10 minutes, add the green beans to the pan and place the salmon fillets on top of the vegetables. Roast for 10–12 minutes, or until the salmon flakes easily and the vegetables are tender and golden.
Squeeze fresh lemon over the salmon before serving. Serve straight from the pan for an effortless, one-pan dinner that feels special.