1. Preheat oven to 375° F. Divide the oil between 2 half-sheet pans. Place chicken breasts on one pan. Season each with 1/2 teaspoon of fajita seasoning. On the other pan, add tomatillos, onion, jalapeños, garlic and lime halves. Roast both pans for 25 minutes.
2. Remove pans from oven. Place tomatillos, half of the onions, jalapeños and garlic in a blender. Add lime juice from 1/2 of the lime, cilantro, salt and pepper. Puree until smooth, and set aside. 
3. Slice the chicken into strips, and place in a bowl. Toss the chicken with half of the tomatillo mixture. Spread out the chicken in a single layer on a sheet pan, along with remaining sliced onions and the bell peppers. Place broiler on high, or heat oven to 500° F. Cook for 5 minutes or until onions and bell peppers begin to char on the edges. Remove from oven. Squeeze the remaining half of lime over the top of all ingredients. Serve with warm tortillas and cotija cheese. Garnish with cilantro and lime wedges. The remaining tomatillo sauce can be served on top of the fajitas or eaten as a salsa with chips. 

Calories: 482, Fat: 18 g (4 g Saturated Fat), Cholesterol: 98 mg, Sodium: 1108 mg, Carbohydrates: 40 g, Fiber: 5 g, Protein: 42 g.