Start by coring and quartering the tomatoes. Add them to a blender along with the chipotle peppers in adobo sauce. Blend until the mixture is smooth and velvety. This is the heart of the sauce, where all that smoky and sweet flavor begins.
Heat olive oil in your skillet or Dutch oven over medium heat. Add the sliced onion and cook until it becomes translucent. Stir in the chopped garlic, letting it sauté briefly until fragrant. Then, add the tomato paste, stirring to coat the onions. You’ll notice the paste deepens in color and adds a savory base for the tinga sauce.
Nestle the chicken thighs into the skillet, surrounding them with the onion mixture. Sprinkle oregano and salt over the chicken before pouring in the blended tomato-chipotle mixture. Cover the skillet and simmer for about 30 minutes. The chicken will absorb all those bold, smoky flavors as it cooks.
Once the chicken is fully cooked, use two forks to shred it directly in the skillet. Stir the shredded meat into the sauce, ensuring it’s fully coated. Taste and adjust the seasoning with more salt if needed.