For the Homemade Fajita Seasoning Blend:
1 tablespoon cornstarch
2 teaspoons chili powder
1 teaspoon kosher salt
1 teaspoon paprika
½ teaspoon sugar
½ taspoon onion powder
½ teaspoon ground cumin
¼ teaspoon garlic powder
¼ teaspoon cayenne pepper

For the Steak Fajitas:
1 clove garlic, minced
1 recipe Fajita seasoning (above)
¼ cup plus 1 tablespoon olive oil, divided
¼ cup fresh cilantro leaves, chopped, plus more for serving
1½ pounds hanger, skirt or flank steak, halved crosswise
2 tablespoons butter
1 sweet onion, halved and sliced vertically
½ teaspoon kosher salt
½ red bell pepper, seeded and sliced into strips
½ orange bell pepper, seeded and sliced into strips
2 wedges of lime
1 avocado, pitted and smashed
16 warm flour tortillas