Preheat oven to 400°F. Line a baking tray with foil and set aside.
Clean brussels sprouts, trim the bottom, and remove any spoiled leaves. Cut sprouts in half lengthwise.
In a large bowl, toss sprouts with olive oil, garlic powder, salt, and pepper.
Add to baking tray in a single layer and bake for 30 minutes.
Increase oven temperature up to 450°F. Sprinkle brussels sprouts with lemon juice if using. Bake for an additional 5-10 minutes to brown, being careful not to burn the sprouts.
Notes
Leftovers will last 3-4 days if sealed in an airtight container in the fridge.