Preheat the oven to 450 degrees Fahrenheit. Line a baking sheet with parchment paper.
Chop off about 2 inches of the ends of the broccolini. In a medium bowl, mix it with with the olive oil and kosher salt.
Place the broccolini on the pan in a single layer. Roast for about 15 minutes, until tender and slightly browned (no need to stir!).
Remove the pan from the oven. Grate the garlic onto the pan, and squeeze on the lemon juice. Use a spoon to gently toss it all together (separating any grated garlic that clumps together). Serve immediately.