Tomato-Watermelon Salad with Feta and Toasted Almonds

INGREDIENTS

• 1 teaspoon (or more) fleur de sel or coarse kosher salt
• 1 cup crumbled feta cheese (about 5 ounces)
• 1/2 cup sliced almonds, lightly toasted
• 1 1/2 tablespoons red wine vinegar
• 3 pounds ripe tomatoes (preferably heirloom) in assorted colors, cored, cut into 1 1/4-inch chunks (about 6 cups)
• 3 tablespoons chopped assorted fresh herbs (such as dill, basil, and mint)
• 8 cups 1 1/4-inch chunks seedless watermelon (about 6 pounds)
• 5 tablespoons extra-virgin olive oil, divided
• 6 cups fresh arugula leaves or small watercress sprigs