1/2 cup water
1/4 cup red wine vinegar
2 tablespoons canola oil
1 tablespoon tomato paste
1 1/2 teaspoons garlic salt, divided
1 teaspoon dried thyme, divided
1/2 teaspoon pepper, divided
1 bay leaf
1 (1 1/2-pound) beef flank steak
In a small bowl, whisk the water, vinegar, oil, tomato paste, 1 teaspoon garlic salt, 1/2 teaspoon thyme and 1/4 teaspoon pepper; add bay leaf. Pour into a large resealable plastic bag.
Score the surface of the steak, making diamond shapes 1/4 in. deep; add to marinade. Seal bag and turn to coat; refrigerate for 3 hours or overnight, turning occasionally.
Coat grill rack with nonstick cooking spray before starting the grill. Drain and discard marinade. Pat steak dry with paper towels. Combine the remaining garlic salt, thyme and pepper; rub over both sides of steak.
Grill steak, covered, over medium-hot heat for 6-8 minutes on each side or until a meat thermometer reaches desired doneness (for medium-rare, a meat thermometer should read 145 degrees F; medium, 160 degrees F; well-done, 170 degrees F). Thinly slice across the grain.