Take 4 to 5 pounds of broccoli or two large bunches and cut into relatively big florets. (There is no need to wash the broccoli first; the oven will kill the bacteria and you want your broccoli very dry to roast well. )
Peel the garlic and cut cloves into thin slices.
Toss broccoli and garlic with approximately 1/2 the oil (just enough to coat), salt, and pepper. Spread in an even layer on a cookie sheet.
Cook in the oven 20-25 minutes or until crisp-tender and the tips of some of the florets are browned. (You may want to turn the broccoli half way through.)
When done, remove from oven and zest lemon over top.
Add juice from the lemon, remaining oil, and Parmesan, and toss to combine.