Preheat grill. Saute 1 thinly sliced red onion in 1/2 cup olive oil in large skillet over medium-high heat until golden and tender (about 3-4 minutes). Add walnuts and garlic, cook stirring occasionally, 3 or 4 minutes until walnuts start to brown. Remove from heat and cool.
Rub steak with Tuscan Herb olive oil, burger blend, and 1/2 teaspoon salt. Grill steak 5-7 minutes on each side or until desired degree of doneness is reached (145-150 degrees for med rare). Remove steak from grill and allow to rest 5 minutes. Slice thin
Whisk together balsamic vinegar and mustard. Gradually whisk in the walnut and oil mixture. Arrange lettuce on serving platter, drizzle with 1/4 cup of the salad dressing mixture. Top with steak slices. Sprinkle on blue cheese. Drizzle the remaining salad dressing and serve.