Start the Cajun rice. Heat 1 tbsp olive oil in the saucepan over medium heat. Add diced onion and bell pepper, sauté until softened (about 3 minutes). Stir in garlic and Cajun seasoning, cooking just until fragrant (30 seconds). Add rinsed rice and toast for 1 minute, then pour in broth. Bring to a boil, reduce heat to low, cover, and simmer for 18 minutes. Remove from heat and let steam, covered, for 5 minutes.
While the rice cooks, mix the blackening spices. In a small bowl, combine smoked paprika, garlic powder, onion powder, thyme, cayenne, salt, and pepper. Press the salmon fillets into the spice mix, coating all sides thickly.
Heat a large skillet over high heat. Add 2 tbsp oil—it should shimmer but not smoke. Carefully place the salmon skin-side up (if skinless, place seasoned side down) in the skillet. Sear for 3-4 minutes until a dark crust forms. Flip gently using tongs and cook the other side for 2-3 minutes, depending on thickness. The salmon is done when it flakes easily but remains slightly pink in the center.