Easy Steak Salad with Lemon Vinaigrette

Name: Easy Steak Salad with Lemon Vinaigrette
Ingredients: Extra virgin olive oil; 1 pound flank steak or skirt steak; Salt and freshly ground pepper; 1/2 head lettuce greens; 1 bunch arugula (young leaves), tough stems removed; 1/2 red bell pepper , thinly sliced lengthwise and cut into 1-inch-long pieces; 4 scallions , thinly sliced; 1 avocado , cut into bite-sized pieces; 4 ounces goat cheese , crumbled; Pomegranate seeds or thinly sliced kumquats (optional); 2 tablespoons lemon juice; 6 tablespoons extra virgin olive oil; 1 teaspoon Dijon mustard (smooth), or 1/2 teaspoon dry mustard; Salt and pepper