Make Southwest Fajita Sauce (recipe below); place in a large bowl. Add beef to sauce in bowl; toss to coat. Cover; marinate in the refrigerator at least 1 hour or up to 4 hours.

In a large wok or skillet over medium-high heat, heat 1 tablespoon oil. Add vegetables. Cook and stir 4 to 6 minutes or until crisp-tender. Transfer vegetables to a bowl; set aside.

Add another 1 tablespoon oil to wok. Transfer half of the marinated beef to wok, allowing marinade to remain in bowl. Cook and stir beef for 2 to 4 minutes or until beef is slightly pink in the center. Transfer cooked beef to bowl with cooked vegetables. Cook remaining beef, still reserving marinade in the bowl.

Add cornstarch to bowl with marinade; whisk until well combined. Push beef to edges of wok. Pour sauce mixture into center of wok. Cook and stir sauce over medium heat just until thickened. Transfer beef and sauce to bowl with cooked vegetables.

5. In wok, heat remaining 1 tablespoon oil. Add cauliflower rice. Cook for 3 to 5 minutes or until crisp-tender, stirring occasionally. Return vegetables, beef and sauce to wok and stir-fry for 1 minute more. Remove wok from the heat and top with green onions and cumin seeds. Serve with chopped fresh cilantro, sliced avocado, lime wedges.