Add the mushrooms and asparagus to a bowl large enough to hold everything with room for tossing later.
Mince up the garlic and the rosemary leaves and add to the bowl. Sprinkle the salt and pepper over everything, and then add in the olive oil.
Cover the bowl with plastic wrap and shake/toss well to coat everything with the herbs, garlic, and oil.
Preheat the oven to 450-degrees
Spread the asparagus and mushrooms in a single layer on a baking pan, making sure to scrape all of the little pieces of garlic out and scattering them around the pan as well
When the oven is heated, put the pan in on the middle rack and roast about 5 minutes to a maximum of 10 minutes. The mushrooms and garlic will soften and brown a little, while the asparagus will still be pretty firm if poked with a fork. If anything, you want to under cook things just a little, as they will continue to cook on the pan once you remove them from the oven…so go for a little bit on the crisp side when you remove them.