In a skillet over medium heat, fry the bacon until evenly brown and crisp. Drain, crumble, and set aside.
Melt the butter and heat the olive oil in a large skillet over medium heat. Mix in the crumbled bacon, garlic, and onion. Cook and stir 2 minutes, then mix in the spinach until evenly coated with the butter and oil. Cover skillet, reduce heat to low, and cook 5 minutes, stirring often, or until spinach is tender. Season with salt and pepper to serve.