Add the olive oil to a skillet over medium heat. Add the apples and onions and cook, stirring occasionally, until softened and lightly browned (about 12-15 minutes).
Meanwhile, trim any fat from the pork tenderloin and then cut it into 1/2" medallions. Season the pork with the garlic powder and some salt & pepper.
Once the apples and onions are cooked, transfer them to a plate.
If the pan is looking really dry, add another small splash of olive oil. Add the pork to the pan and cook on each side for about a minute, then transfer it to the same plate as the apples and onions.
Increase the heat to medium-high and add the brandy to the skillet. Let it bubble until reduced by half (about 1-2 minutes), scraping up the browned bits from the bottom of the pan.
Stir in the cream, then add the pork, apples, and onions back into the pan.
Cook for another five minutes or until the pork is cooked through and the sauce has thickened up a bit (reduce the heat as needed so it's bubbling but not boiling furiously).
Season with extra salt & pepper as needed and serve immediately.