Preheat the oven to 400°F (200°C). Line an 11x17-inch baking sheet with foil or parchment paper, and lightly grease it with cooking spray.
In a small bowl, stir together 2 teaspoons ground cumin, 2 teaspoons chili powder, 1 teaspoon onion powder, 1 teaspoon salt, and 1 teaspoon crushed red pepper flakes.
Thinly slice 4 boneless skinless chicken breasts into pieces that are about 2 inches long and no thicker than 1/4 of an inch. Place in a large mixing bowl.
Core and slice 3 large multi-color bell peppersand slice the 1 medium red onion. Add to the bowl with the chicken along with 2 cloves minced garlic.
Drizzle 2 tablespoons olive oil over the sliced chicken and vegetables. Sprinkle the fajita seasoning over the mixture. Toss everything together until the chicken and vegetables are evenly coated with the seasoning.
Spread the seasoned chicken and vegetables in a single layer on the prepared baking sheet. Make sure to drizzle any remaining oil from the bowl onto the sheet for extra flavor.
Place the baking sheet in the preheated oven. Cook for 15 minutes, then carefully stir the chicken and vegetables. Continue cooking for an additional 5-10 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the vegetables are softened and slightly browned.
Once cooked, remove the baking sheet from the oven. Drizzle 1/4 cup lime juice over the chicken and vegetables, and toss to combine.
Warm the flour tortillas and serve the chicken and vegetables in them. Optionally, top with sour cream, fresh cilantro, guacamole, or salsa.
Notes
To warm tortillas on the stovetop: Use a small skillet over medium-high heat, warming each tortilla for around 30 seconds per side until they’re soft.To warm tortillas in the microwave: Stack them between damp paper towels and microwave in 20-second intervals until fully warmed.To warm tortillas in the oven: Wrap a stack of tortillas in aluminum foil and heat at 350°F for 10-15 minutes.