Preheat oven to 275°F. Whisk oil, maple syrup, and cardamom in a small bowl. Place salmon in a large baking dish and brush with cardamom syrup on all sides. Marinate at room temperature 30 minutes. Season each side of salmon with 1 tsp. salt. Bake until salmon is firm but still pink in the center, 22–25 minutes (if you prefer salmon more well done, cook an additional 5 minutes). Flake salmon into large pieces and arrange on a platter. Top with dill, if using.