Heat oven to 375° F.
Place the salmon in a glass baking dish. Add the bay leaves and enough water to reach halfway up the sides of the fillets. Bake until the salmon is the same color throughout and flakes easily, about 15 minutes. Transfer to a plate; let cool.
Meanwhile, working over a bowl, cut each grapefruit segment from its surrounding membranes. Squeeze the membranes to release any remaining juice. Add the vinegar, oil, sugar, and salt to the juice. Pour all but 1 tablespoon of the vinaigrette into a large resealable plastic bag. Add the salmon to the bag and refrigerate for at least 1 hour.
To serve, add the grapefruit segments, cucumber, and watercress to the reserved vinaigrette in the bowl and toss. Drain the salmon. Divide the rice among individual plates and top with the watercress salad and salmon.
Tip: To section a grapefruit, peel it, then use a sharp knife to cut between each section, close to the membrane. Remove the segments intact.