To prepare the chicken, in a large sealable plastic bag or in a shallow baking dish, combine the chicken, garlic powder, onion powder, cumin, paprika, chili powder, pepper, lime juice and vegetable oil. Seal the bag and mix everything together. If you are using a baking dish, use tongs to work the spices evenly into the chicken. Let stand for 1 hour. 

Heat a large fry pan over medium-high heat. Add the chicken and cook, turning once, until browned and cooked through, about 15 minutes. Transfer the chicken to a cutting board and let rest for 10 minutes, then shred the meat.

To prepare the toppings, in a small bowl, stir together the onion, cilantro, jalapeño and lime juice. Season to taste with salt and pepper.

While the chicken rests, wipe the fry pan clean with a paper towel, then heat the pan over medium-high heat. Stack 2 tortillas in the pan and cook until the underside starts to char. Flip the tortillas over and cook the other side. Repeat with the remaining tortillas. (The 2 tortillas aren't a must, but they help to keep all the taco fillings in.) 

Top the tortillas with the chicken and onion-cilantro mixture. Serve with the lime wedges for squeezing over the tacos.