Make the dressing: in a blender, combine avocado, lime juice, olive oil, salt, pepper, garlic powder, and cayenne. Blend until smooth. Add water 1 tbsp at a time if too thick.
Coat the chicken: in a large bowl, add shredded chicken. Pour dressing over and stir gently until evenly coated.
Add veggies: add diced avocado, halved tomatoes, red onion, and cilantro. Toss gently just until combined. Do not overmix.
Taste and adjust: season with salt and pepper. Add more lime or water if needed for consistency.
Serve: serve in bowls, over greens, in a wrap, or in a lettuce cup. Top with jalapeño if desired.