Add the bacon in an even layer to a medium non-stick skillet. Place over medium heat. Cook, turning halfway through, until bacon is crisp and golden, about 8 minutes. Remove bacon to a paper towel lined plate.
If necessary, drain all but 1 tablespoon of the bacon fat and return skillet to medium-high heat. Add the chicken breast and cook, stirring a few times, until cooked through and golden, about 4 minutes.
Add the taco seasoning and ¾ cup water. Continue to cook, stirring, until sauce coats chicken, 1 minute more. Remove from the heat.Arrange the taco shells on a plate and microwave on high 40 to 60 seconds.
Fill warm taco shells with chicken mixture. Top with shredded lettuce, shredded cheese, chopped tomatoes, and chopped green onion. Drizzle with ranch dressing. Crumble bacon over top. Serve immediately.