Beef and Pepper Fajitas

2 limes
1 garlic clove, crushed with garlic press
2 tablespoons plus 3â„4 teaspoon chili powder
1 tablespoon plus 1â„2 teaspoon brown sugar
3â„4 teaspoon salt
1 beef flank steak (about 1 pound), trimmed
2 teaspoons olive oil
1 large red pepper, thinly sliced
1 large green pepper, thinly sliced
1 large red onion, cut in half and thinly sliced
6 burrito-size flour tortillas, warmed accompaniments: salsa, light sour cream, cilantro leaves (optional)

In large bowl, mix garlic, lime peel, 2 tablespoons lime juice, 2 tablespoons chili powder, 1 tablespoon sugar, and 1â„2 teaspoon salt until blended. Add steak to bowl and rub all over with chili-powder mixture. Marinate steak 15 minutes at room temperature or up to 1 hour in the refrigerator.
Heat grill pan over medium-high heat until hot.Add steak and cook 20 to 25 minutes for medium-rare or until of desired doneness, turning steak over once (reduce heat to medium if steak browns too quickly).
Meanwhile, in nonstick 12-inch skillet, heat oil over medium heat until hot. Add peppers and onion and cook covered, 10 minutes, stirring occasionally. Add remaining 3â„4 teaspoon chili powder, 1â„2 teaspoon sugar, and 1â„4 teaspoon salt, and cook 5 minutes longer, uncovered, or until vegetables are tender and golden, stirring occasionally. Stir in remaining 1 teaspoon lime juice.
Transfer steak to cutting board; let stand 10 minutes to allow juices to set for easier slicing. Thinly slice steak and wrap in tortillas with pepper mixture. Serve with salsa, sour cream, and cilantro if you like.