Preheat the oven to 400°F. Spray a large baking sheet with gluten-free nonstick cooking spray.
Wash and pat dry the broccolini, then place on the baking sheet in a single row (not on top of each other). Drizzle with olive oil and balsamic vinegar. Spread minced garlic evenly over top, then sprinkle with salt.
Roast for 20-25 minutes, depending on how soft you like your broccolini (I prefer mine a bit on the crunchy side). Remove from the oven and garnish with red pepper flakes, to taste.