Preheat the oven to 425 degrees. Line a rimmed baking sheet with aluminum foil.
Cut the head of broccoli into 1-inch florets. You should have about 6 overflowing cups once it's all chopped up. Trasnfer to a large mixing bowl.
Add the garlic and olive oil to the broccoli and toss until evenly coated in the oil. Sprinkle in salt, pepper, and red pepper flakes (if using) over the veggies and toss to combine. Spread broccoli florets onto the prepared baking sheet in an even layer.
Roast for 10 minutes, stir the broccoli, then roast for an additional 5 to 10 minutes, until edges are browned and broccoli is crispy. Remove from the oven and serve warm.