Prep the salmon. Pat the salmon dry with paper towels. Sprinkle both sides with 1 tablespoon Cajun seasoning and a pinch of salt and pepper.
Let it sit while you prep the other ingredients so the spices hydrate.
Cook the pasta. Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.
Toss pasta with a splash of olive oil to prevent sticking.
Sear the salmon. Heat 1 tablespoon olive oil in a large nonstick skillet over medium-high. Place salmon skin-side down and cook 4–5 minutes until the skin is crisp. Flip and cook 2–4 minutes more, depending on thickness, until just opaque in the center.
Transfer to a plate and tent with foil.
Build flavor in the pan. Lower heat to medium. Add 1 tablespoon butter to the same skillet. Stir in the minced garlic and cook 30 seconds until fragrant.
Sprinkle a small pinch of Cajun seasoning if you like extra flavor.
Make the lighter Alfredo base. Pour in the broth and milk. Bring to a gentle simmer, whisking to pick up browned bits. Let it reduce for 3–4 minutes until slightly thickened and steamy, not boiling hard.
Finish the sauce off-heat. Turn the heat to low.
Whisk in the Greek yogurt until smooth. Add grated Parmesan and stir until melted and creamy. If the sauce seems too thick, add splashes of the reserved pasta water.
Season with salt, pepper, and a squeeze of lemon juice. Taste and adjust.
Add veggies (optional but recommended). Stir in baby spinach until just wilted, or fold in warm steamed broccoli florets. The greens balance the richness and add color.
Toss with pasta. Add the drained pasta to the skillet and toss until well coated.
If needed, loosen with more pasta water to reach a silky consistency that clings to the noodles.
Flake in the salmon. Gently flake the salmon into bite-size pieces, discarding the skin if you prefer. Fold into the pasta so you keep big, tender chunks. Finish with lemon zest, parsley, and red pepper flakes if you like heat.
Serve. Plate immediately while hot and creamy.
Top with a final sprinkle of Parmesan and a light dusting of Cajun seasoning for color.