Preheat the oven to 400°F (200°C) °F. Line a rimmed sheet pan with parchment paper or lightly oil it.
Mix the lemon mayo: In a small bowl, combine 3 tablespoons mayonnaise or lemon aioli, 1 teaspoon finely chopped or grated garlic, and 2 teaspoons fresh lemon juice. Set aside.
Make the spice blend: Stir together 1 teaspoon dried oregano, ¼ teaspoon smoked paprika, ½ teaspoon freshly ground black pepper, ¼ teaspoon red pepper flakes and ½ teaspoon kosher salt in a small bowl.
Toss the broccolini with a little olive oil, salt, and pepper. Spread it out around the edges of the sheet pan.
Place 2 pounds salmon fillet* skin-side down in the center of the pan. Rub the spice mix into the flesh. Spoon the lemon mayo on top and spread it evenly.
Roast everything together for 15–20 minutes, or until the salmon is opaque and flakes easily (internal temp should be ~120°F/50°C for medium-rare or ~140°F/60°C for well done). The broccolini should be tender and slightly crispy at the tips.
Squeeze fresh lemon over the salmon and broccolini.
Serve and enjoy!