Step 1

Place 2 teaspoons chili powder, 2 teaspoons ground cumin, 1 teaspoon garlic powder, 1/2 teaspoon paprika, 1/2 teaspoon oregano, 1/2 teaspoon kosher salt, and 1/4 teaspoon black pepper in a medium bowl and stir to combine. Add 1 pound boneless, skinless chicken breasts and toss to coat evenly with the seasonings.

Step 2

Prepare the toppings and tortillas: Warm 12 to 16 small flour tortillas one at a time by holding them directly over a medium flame on a gas stove, or in a skillet over medium heat, flipping occasionally, until charred in spots and pliable. Stack and wrap in a clean kitchen towel or aluminum foil to keep warm. Cut romaine or iceberg lettuce into fine shreds.

Step 3

Heat 2 tablespoons of the olive oil in a large skillet (preferably cast iron) over medium heat until shimmering. Add the chicken and cook until blackened in spots and cooked through (an internal temperature of at least 165ºF), 7 to 10 minutes per side. Meanwhile, prepare the vegetables.

Step 4

Halve and cut 1 large white or yellow onion into 1/4-inch slices (about 2 cups). Trim and cut 2 medium red bell peppers and 1 medium green bell peppers into 1/4-inch slices (about 4 1/2 cups total). Trim and thinly slice 1 medium jalapeño pepper crosswise if desired. Halve 1 medium lime; cut one half into wedges and reserve for serving.

Step 5

When the chicken is ready, transfer to a clean cutting board. Add the remaining 1 tablespoon olive oil, onion, and peppers (including jalapeño) to the pan. Season lightly with kosher salt. Cook, stirring frequently, until softened and browned in spots, 5 to 8 minutes. Turn off the heat.

Step 6

Slice the chicken breasts crosswise into 1/4-inch pieces and add to the skillet. Squeeze the lime half over the fajita mixture and toss to combine. Serve in flour tortillas with the reserved lime wedges and desired toppings.