1. In a blender, mini-chop, or food processor, pulse the sun-dried tomatoes, chipotle, adobo sauce, water, oil, vinegar, mustard, and brown sugar together until smooth. Season with salt and pepper to taste and pulse again. Transfer to a small bowl.
2. In another small bowl, mash the avocado with half the cilantro and all of the lime juice. Season generously with salt and pepper to taste.
3. Spread 4 of the slices of bread with the avocado mixture. Spread the remaining 4 pieces of bread with the sun-dried tomato-and-chipotle mixture, then layer on the chicken, bacon, tomato, onion, the remaining cilantro, and the bread. Cut in half and serve immediately.