Combine salsa ingredients in a medium bowl and set aside in the fridge.
Heat olive oil in large skillet over medium heat. Add steak and red onions, season with salt and pepper, and cook until steak is mostly cooked through. Add garlic and sauté another 30 seconds.
Add remaining filling ingredients and simmer for 3-5 minutes, or until steak is cooked through and barbecue sauce is warmed. Remove from heat and stir in 1/2 cup cheese. Taste and adjust seasonings and heat as desired.
Preheat oven to 350 degrees and line a baking tray with foil and place a baking rack on top of it.
Divide flauta filling evenly between tortillas and roll as tightly as possible. If you like, save some of the filling to be served on top of the flautas. Optionally, cut off about 1/3 of the tortillas before rolling if you want less tortilla.
Brush both sides of each flauta lightly with olive oil, and place on rack, seam side down.
Cook flautas for 10 minutes, then turn oven to broil. Broil flautas until golden brown, 2-3 minutes, watching closely so they don’t burn. Flip flautas over and broil the other side until crispy.
Top individual servings of flautas with more filling or barbecue sauce and pineapple salsa.
Cook's note: This filling and salsa is so delicious, it would also be great served over rice rather than wrapped in the flautas.
This recipe made 8 flautas (2 per person). You could use smaller tortillas for more flautas. Serves 4.