Cook the chopped bacon in a large skillet over medium heat until crispy. Remove and set aside.
In the same skillet, add diced onions and sauté until soft.
Stir in the minced garlic and cook for another 30 seconds.
Add the trimmed green beans to the skillet and stir to coat.
Season with salt, pepper, and red pepper flakes, then cover and cook for 7-10 minutes until tender.
Stir in the cooked bacon and butter, mix well, and serve warm.