Heat a wide, deep frying pan over medium-high heat. Add fennel seeds and toast until fragrant. Arrange salmon over toasted fennel and add broth, white wine, lemon juice, rosemary sprig, and bay leaf. Bring to a simmer, then cover and cook until salmon is no longer translucent but still moist in the center, 2 to 4 minutes total. (It will continue to cook as it sits.)
Meanwhile, in a medium bowl, toss spinach, beans, radishes, 1/4 cup oil, the vinegar, garlic, chopped rosemary, and salt and pepper to taste. Divide salad among 4 wide, shallow bowls. Gently lift salmon fillets from poaching liquid and place each on a salad.
Pour about 1/2 cup poaching liquid into each bowl. Drizzle salmon with remaining 1 tbsp. oil and sprinkle with rosemary blossoms, if using.