Slice the chicken into thin strips and add directly onto a sheet pan.
Slice the onion and peppers into strips and add them to the pan.
Season with all the spices, drizzle with oil, and toss everything together really well.
Spread into an even layer and bake in a preheated 425°F oven for 20–25 minutes.
Mash the avocados and mix with the onion, Serrano chili, cilantro, lime juice, and salt.
Give the chicken and vegetables a quick toss, then broil for another 2–3 minutes until slightly charred.
Serve in warm tortillas with fresh guacamole, cilantro, and an extra squeeze of lime.
