Start by mixing all the dry seasonings in a small bowl: salt, ground cumin, garlic powder, and taco seasoning. Use this spice mix to season the chicken and vegetables separately. In a bowl, season the thinly sliced chicken breasts with most of the spice blend, 1 tablespoon of vinegar, and 1 teaspoon of olive oil. Toss to coat well and set aside. Reserve the remaining seasoning to use on the vegetables later.
Heat a grill pan or non-stick skillet over medium-high heat. Once hot, add the seasoned chicken and cook for about 4–5 minutes on one side. Flip and cook the other side for another 3–4 minutes, or until the chicken is golden brown and fully cooked. Remove the chicken from the pan and set aside.
In the same pan, add the sliced bell peppers and onions along with the remaining seasoning. Sauté over medium-high heat for 6–8 minutes, stirring occasionally, until the vegetables are tender and slightly caramelized.
Return the cooked chicken to the pan with the vegetables. Toss everything together and cook for an additional 1–2 minutes, just until everything is heated through and well combined.
Serve hot with your choice of toppings like diced tomatoes, avocado, a spoonful of Greek yogurt, or a warm tortilla.