Prepare all of the ingredients. Preheat oven to 425deg.
Add brats, garlic cloves and beer to bowl and let marinade for 30 minutes.
In a bowl, combine potatoes, half of oil, and seasonings. Toss to coat. Pour contents into a mostly single layer on a large baking sheet. Place in oven for 30 minutes (while brats are marinating).
In the same bowl, add remaining oil, onions, bell peppers and mushrooms. Toss to coat. After 30 minutes of baking, remove potatoes from oven and cover with veggie mixture.
Remove brats from beer, and add, evenly spaced, on top of potato & pepper mixture. Place in oven and cook for and additional 30 minutes.