Combine broth, onion, garlic, peppercorns and red pepper flakes in a straight-sided sauté pan. Cover and bring to a boil, then reduce heat to medium. Simmer 5 minutes. Season salmon with salt and add to pan. Cover and cook at very low simmer for 5 minutes. Remove fish to a plate with a large spatula and refrigerate at least an hour.
In a small bowl, whisk together orange juice, vinegar, mustard, 1/2 tsp of the salt and the hot sauce. While whisking, add olive oil in a thin stream.
Combine kale, grapes and sunflower seeds in large bowl. Remove salmon skin. Flake salmon into bite-size pieces and add to bowl. Pour dressing over salad and season with remaining 1/4 tsp salt. Gently toss to combine.
Poach salmon the night before and refrigerate, tightly wrapped in plastic, until serving.
