Heat 1 tablespoon oil in a large skillet over medium-high heat; add chicken breasts.
Cook 6 to 7 minutes on each side or until done.
Remove from pan; cool and shred chicken.
Heat remaining 1 tablespoon oil in skillet over medium-high heat.
Add onion and garlic; cook 4 minutes or until tender.
Add tomatoes and red pepper; cook for 15 minutes or until most of liquid evaporates.
Remove from heat, and stir in shredded chicken and green chiles.
Melt butter in a heavy saucepan over low heat.
Add flour and fajita seasoning; whisk until smooth.
Cook 1 minute, whisking constantly.
Gradually add half-and-half; cook over medium heat 4 minutes or until thick and bubbly, whisking constantly.
Spread one-fourth white sauce in a lightly greased 13- x 9-inch baking dish.
Arrange 6 tortilla halves over sauce.
Top with half of chicken mixture and ⅔ cup cheese.
Repeat layers once, ending with cheese.
Spoon one-fourth sauce over the cheese, and top with remaining tortilla halves.
Spoon remaining sauce over tortillas.
Reserve remaining ⅔ cup cheese.
Bake, uncovered, at 350° for 40 minutes or until thoroughly heated.
Sprinkle with reserved ⅔ cup cheese, and bake 5 more minutes.
Garnish, if desired.
