Place a skillet over medium-high heat oil and melt butter. Season the shrimp with salt and pepper. Arrange the shrimp on a single layer in the skillet and cook for about 2 minutes on both sides. Remove to a plate and set aside.
Add a tablespoon of oil if need be, allow the skillet to get hot, add the pepper and onion, season with salt and pepper, cook for a couple of minutes until it softens.
Add pineapple and allow it to soften for about 1-2 minutes. Add the shrimps, and green onions and stir.
Add the barbecue sauce, stir, allow the mixture to simmer making sure everything is well combined.
Add red pepper flakes if you're using, simmer for an additional one minute, remove from the heat.
Serve and enjoy!