Preheat your oven to 450 degrees F. Line a rimmed baking sheet with parchment paper and place it on the lower third of the oven.
In a large bowl, combine the frozen broccoli florets with olive oil, optional sugar, kosher salt, black pepper, and optional red pepper flakes. Toss well.
Spread the broccoli in a single layer on the preheated baking sheet.
Bake on the lower third rack for 16 to 18 minutes until tender and the edges are browned. For extra crispness, broil for 1 to 2 minutes.
Squeeze fresh lemon juice over the broccoli. Serve immediately.