Coat both sides of tortillas with nonstick cooking spray. Stack and cut into 8 wedges. Push wedges into muffin cups. Bake for 6-8 minutes or until crispy and golden brown.
Mash avocado, sour cream, tomato, lime juice, garlic, and cilantro together in small bowl. Salt to taste and chill.
Cook ketchup, sugar, chipotles, soy sauce, vinegar, chili powder, and chicken in a medium saucepan over medium-low heat for 8 minutes, or until sauce is syrupy.
Top each tostada with 1 tsp of avocado mixture, then 1-2 TBSP chicken mixture.
Garnish each tostada with a small dollop of sour cream, cilantro and lime zest.