Preheat oven to 400°F. Lightly grease large, rimmed sheet pan or line with parchment paper.
Spread peppers and onions on pan in a single layer. Drizzle over olive oil and toss to coat. Push vegetables to the sides and lay chicken breasts flat in center of pan. Sprinkle garlic powder, onion powder, salt and pepper evenly over vegetables and chicken. Brush each chicken breast thickly with 1 tablespoon adobo sauce.
Bake for 20 -25 minutes until chicken reaches internal temperature of 165°F using an instant read thermometer placed in the thickest part of the chicken. Vegetables will be tender and starting to brown.
Remove pan from oven. Slice chicken into thin strips lengthwise. Pile chicken and vegetables onto tortillas to build fajitas. Add toppings as desired.
Store leftovers in airtight container in refrigerator for up to 3 days.