• Heat olive oil in a large saucepan over medium heat. Add onion; cook and stir until it begins to soften, about 2 minutes. Add garlic and stir until fragrant, about 30 seconds. Add broth, tomatoes along with their juices, cumin, oregano, chipotle hot sauce and chili powder; bring to boil. Add chicken breasts and season lightly with salt and pepper. Stir to coat chicken with tomato mixture, then spread chicken breasts into an even layer. Reduce heat and cover; keep at a low simmer for 20 to 25 minutes, flipping breasts once about half way through, until chicken is tender and easy to shred.
• When chicken is nearly tender, preheat oven to 300 °F (149 °C) and wrap 2 stacks of 6 tortillas each in aluminum foil.
• Once chicken is tender, transfer to cutting board. Leave saucepan on stovetop, increase heat to medium-high and return sauce to boil. Cook uncovered, stirring occasionally, until the liquid has mostly evaporated (it should look like a thick salsa), 8 to 12 minutes. Remove from heat.
• While sauce reduces, shred chicken with two forks and warm foil wrapped tortillas in preheated oven (10 to 15 minutes).
• Once sauce has reduced, stir in shredded chicken and place over medium heat; cook and stir until just heated through.

To Assemble Tacos

• Divide chicken among warmed tortilla and top with cheese, avocado and onion. Garnish with cilantro and serve with lime wedges if desired.