Preheat oven to 425°F (220°C). Line a sheet pan with foil and lightly oil it.
Toss canned chicken with barbecue sauce, olive oil, salt, and pepper in a bowl.
Spread chicken, sliced onion, and bell pepper on the sheet pan in an even layer.
Roast 12–15 minutes until edges caramelize and veggies soften; stir once halfway through.
Warm tortillas in the oven 1–2 minutes at the end, then top with chicken mix and sprinkle cheese.
Fold tacos, add cilantro, lime, and sour cream to taste, and serve immediately.