Preheat oven to 350°F. Lightly grease a 9×13-inch baking dish.
Bring a large pot of salted water to a boil. Add green beans and blanch until bright green and just tender, 3 to 4 minutes. Drain well and pat dry.
In a skillet over medium heat, cook chopped bacon until crisp, 8 to 10 minutes. Transfer bacon to a paper-towel-lined plate; discard excess drippings.
In a bowl, whisk together melted butter, brown sugar, soy sauce, garlic, salt, black pepper, and red pepper flakes until smooth.
Add blanched green beans and cooked bacon to the baking dish. Pour the brown sugar butter mixture over the top and toss to coat evenly.
Bake for 25 to 30 minutes, stirring once halfway through, until the sauce is bubbling and slightly thickened and the beans are tender.
Let rest 5 minutes for the glaze to set. Toss again and serve warm.
Notes
Make ahead: blanch beans and cook bacon up to 1 day in advance; keep refrigerated. For extra sticky glaze, use dark brown sugar. Swap soy sauce with Worcestershire for a different savory note. Line the dish with foil for easier cleanup.