Preheat a large nonstick saute pan, or preheat a grill or grill pan. Sear the flank steak on both sides for 3 to 4 minutes on each side or until medium-rare. Remove steak from heat and let rest for 10 minutes.
Meanwhile, combine vegetables, vinegar, olive oil, lime juice, cilantro, chili powder, salt, and pepper in a large bowl and mix well.
Cut steak against the grain into slices. Serve the steak and vegetable salsa with tortillas, chips and avocado, sour cream, and grated Cheddar, if desired.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.