Steak Fajitas with Lime Juice

Ingredients

• 4 Tbsp. fresh lime juice, divided
• 1 large onion (5.3 oz.) cut in half and thinly sliced
• 4 tsp. (4 cloves) garlic, minced
• 1 1/2 tsp. dried chili powder
• 2 lbs. top round beef
• fat free olive oil spray
• 4 8-inch whole wheat tortillas (soft tacos)
• 1 cup shredded cilantro
• 1 whole medium tomato (about 4.5 oz.), chopped