In a large, ziplock bag, combine the chili powder, cumin, garlic, and Sriracha. Add 2 tablespoons vegetable oil to the bag and mix to combine. If the chicken breasts are not uniform in size, place them in a clean ziplock bag and gently pound with a rolling pin to an even thickness. Add the chicken to the marinade, turning once or twice, and set aside while preparing the vegetables.
Heat a large cast iron or nonstick skillet over medium-high heat. Add 1 tablespoon of vegetable oil and heat until shimmering. Add the chicken breasts and cook, undisturbed, for about 4-5 minutes or until seared on one side. Turn the chicken over and continue cooking until browned and cooked through, about 4-5 minutes more. Remove the chicken from the skillet and set aside tented with foil to keep warm. Carefully and lightly, wipe out any large, burnt chunks from the skillet with paper towels.
Add the last 1 tablespoon vegetable oil to the skillet and heat. Add the vegetables and cook, stirring occasionally, until the vegetables are soft and beginning to brown, about 7-10 minutes.
Remove the vegetables from the heat and stir in the lime juice. Slice the chicken and add to the vegetables, squeeze on a little more lime juice and serve immediately with warm tortillas.