Combine 1/3 cup red onion and all remaining salsa ingredients to 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 taquito filling ingredients (except for cheese) and simmer for 3-5 minutes, or until steak is cooked through and barbecue sauce is warmed. Remove from heat and stir in 1 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 taquito filling evenly between tortillas and roll as tightly as possible. Brush both sides of each taquito lightly with olive oil, and place on rack, seam side down.
Cook taquitos for 10 minutes, then turn oven to broil, adjusting oven rack to top middle position. Broil taquitos until golden brown, 2-3 minutes, watching closely so they don’t burn. Flip taquitos over and broil the other side until crispy. Push taquitos together and top with cheese. Broil until cheese is melted.
Top individual servings of taquitos with more barbecue sauce and pineapple salsa.