Nicoise Salad with Grilled Tuna

Name: Nicoise Salad with Grilled Tuna
Ingredients: 1 medium red onion, diced; 4 fresh tuna steaks, about 6 ounces each; 1 tablespoon pure olive oil; Kosher salt and freshly ground black pepper to taste; 2 cups arugula, washed and dried; 1-1/4 cups basil vinaigrette (recipe follows); 6 ounces cooked green beans; 1-1/2 cups marinated baby artichokes, drained; 8 ounces small red potatoes, diced and cooked; 1 pound vine-ripened tomatoes, cored and diced; 1 large fennel bulb, very thinly sliced; 1 tablespoon Dijon mustard; 2 tablespoons white wine vinegar; 1/2 teaspoon kosher salt; Freshly ground black pepper; 1/4 cup prepared basil oil; 3/4 cup extra-virgin olive oil