Preheat your oven to 375°F. Line a large baking sheet with parchment paper for easy cleanup.
Spread out the diced chicken breasts on one side of the baking sheet.
Place the sliced red bell pepper and zucchini on the other side of the sheet.
In a small bowl, mix together the olive oil, salt, oregano, cumin, paprika, cayenne, and black pepper. Drizzle this mixture over the chicken and veggies, then toss to ensure everything is well coated.
Place the sheet pan in the oven and bake for 10-15 minutes, or until the chicken is cooked through and the veggies are tender.
While the fajita mix is cooking, warm the tortillas, and slice the avocado.
To serve, load the chicken and veggies onto warm tortillas, top with slices of avocado, and drizzle with BBQ sauce if desired.