Preheat oven to 400°F. Line a baking sheet with parchment paper or use nonstick cooking spray.
Make the taco spice mix by adding 2 tsp chili powder, 1 tsp onion powder, 1 tsp garlic powder, 1 tsp paprika, ½ tsp cumin, ½ tsp salt, and ½ tsp ground black pepper to a bowl. Mix together.
Add 1 sliced green, yellow and red bell pepper, 1 sliced yellow onion, and 2-3 sliced raw chicken breasts to a large bowl. Drizzle 2 Tbsp olive oil and sprinkle the taco spice mix over top of everything and toss together until evenly coated.
Spread the ingredients onto the prepared baking sheet in an even layer. Bake at 400°F for 12 minutes, then remove and flip everything over using a spatula. Cook another 12 minutes, or until the chicken is fully cooked and reaches an internal temperature of 165℉ using a meat thermometer.
Add the mixture to a large bowl and serve with taco shells or over rice. Add any favorite toppings including salsa, sour cream, or guacamole.