2-1½ pound top sirloin steaks (or 2-3 pound steaks, 1” thick)
6 tablespoons olive oil
2 tablespoons balsamic vinegar or red wine vinegar
6 garlic cloves, minced
1 large onion, sliced
1 large red bell pepper, sliced
1 large green bell pepper, sliced
1 cup unsalted beef broth or low-salt chicken broth
Place steaks in glass baking dish. Mix 4 tablespoons oil, vinegar and half of garlic in small bowl. Pour over steaks, turn to coat. Marinate 30 minutes at room temperature or refrigerate 3 hours.
Heat 2 tablespoons oil in large iron skillet over medium heat. Add onion, bell peppers and remaining garlic, and sauté 8 minutes. Add broth, increase heat and boil until vegetables are tender and liquid thickens slightly, about 5 minutes. Season with salt and pepper. Grill steaks until cooked as desired, about 5 minutes.