Mist a large nonstick skillet with cooking spray and heat on medium-high. Add beef and cook, breaking up with a wooden spoon, until browned, about 3 minutes.
Mist a 3- to 3 1/2-qt slow cooker with cooking spray. Add beef, tomatoes, onion, poblano, zucchini, chile powder and cumin; stir to combine. Cover and cook until onion softens, 2½ hours on high or 5 hours on low.
Stir in cilantro and salt. Warm tortillas according to package directions. To assemble, top each tortilla with beef mixture, lettuce and sour cream, dividing evenly.
Warm corn tortillas envelop tender shreds of nutty chicken in this unexpected slow-cooker creation. A tangy fresh mint and cucumber topping brings the Thai-Mexican mingling together for an exotic, spicy meal.
The rich, deep flavor of braised beef is a perfect match for the subtle, sweet smokiness of ancho chiles. These melt- in-your-mouth tacos serve a crowd and can be made ahead – they’re tailor-made for a taco party!