1. Cook chicken with garlic, salt, and pepper in large skillet with vegetable oil. Cook until chicken is no longer pink.
2. While chicken mixture is cooking, spread about 1 teaspoon of butter on one side of each tortilla shell.
3. Drain chicken mixture. In same (unwashed) skillet, off heat, lay one tortilla shell butter-side down. Spread on tortilla 1/2 cup of shredded cheese. Next spread 1/4 of chicken mixture. Next spread another 1/2 cup of shredded cheese. Place another tortilla shell on top, butter-side up.
4. Place back on heat, medium. Cook each tortilla, about 3 minutes on each, butter-side.