Preheat your oven to 425°F and position the rack in the upper-middle position. This high temperature is crucial for caramelizing the peppers and onions while the beef cooks through properly.

Pat the sirloin steak strips dry with paper towels and place them in a large bowl. Combine chili powder, cumin, paprika, oregano, salt, and black pepper in a small bowl, then toss the beef strips with this spice mixture until evenly coated.

Arrange sliced bell peppers and onions across two large sheet pans, drizzling with 2 tablespoons of olive oil and sprinkling with salt. Roast for 8 minutes until they begin to soften and develop golden edges.

Remove the sheet pans from the oven and push the vegetable mixture to the sides, creating space in the center. Add the remaining 1 tablespoon olive oil to each pan, then arrange the seasoned beef strips in a single layer down the middle.

Scatter minced garlic over the loaded sheet pan beef fajitas, drizzle with lime juice and beef broth, then return to the oven for 7 minutes until the beef reaches your desired doneness.

Remove from heat and top with fresh cilantro and shredded cheddar cheese, allowing it to melt slightly from the residual heat. Stir gently to combine all elements while keeping the beef and vegetables intact.

Warm your flour tortillas in a dry skillet or directly over a gas flame for 30 seconds per side. Serve the sheet pan mixture alongside tortillas, sour cream, and additional cilantro for customizing individual fajitas.