- In a large skillet, cook the onion in the oil over medium heat until crisp-tender and just beginning to brown, about 5 minutes. Stir in the salsa, tomatoes with their juice and the vinegar. Simmer, stirring regularly until quite thick, about 5 minutes. Stir in the chicken, cool, then taste and season with salt.
- Serve the mixture in warm tortillas. Let guests add avocado, cheese and cilantro to taste.
For tostadita appetizers, arrange 24 thick tortilla chips on one or more serving platters. Top each with a heaping tablespoon of the chicken tinga, a few pieces of avocado, a sprinkling of cheese and cilantro, and they’re ready to pass around.