In a large bowl, whisk together ¾ cup lime juice, tequila, garlic powder, cumin, steak seasoning, oregano, pepper and red pepper flakes. Place steak in a shallow dish; add tequila mixture and turn to coat. Refrigerate, covered, 8 hours or overnight, turning once.
Drain beef, discarding marinade; pat dry. Grill, covered, over direct medium-high heat, turning once, until desired degree of doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°), 10-15 minutes. Place beef on cutting board; cover and let rest 5-10 minutes. Thinly slice steak across the grain.
Place salad mix on serving platter; drizzle with olive oil and the remaining 1 tablespoon lime juice. Place steak over romaine; top with tomatoes and, if desired, cotija cheese and lime wedges.
4 ounces cooked steak with 1-½ cups salad: 257 calories, 11g fat (5g saturated fat), 72mg cholesterol, 243mg sodium, 8g carbohydrate (2g sugars, 2g fiber), 31g protein. Diabetic Exchanges: 4 lean meat, 1-½ fat, 1 vegetable.
