Melt the bacon grease in a large skillet over medium heat.
Add the potatoes and onions to the skillet and cook, stirring occasionally, until the onions begin to soften, about 5 to 7 minutes.
Add in the garlic powder, salt, and pepper, stirring to combine. Cook until the potatoes are tender and browned, about 10 to 15 minutes, stirring occasionally but allowing the potatoes to sit long enough to brown.
Notes
Don't want to render your own bacon fat? You can buy bacon grease at many grocery stores. BaconUp is a common brand.
If you want to cook your own bacon to get the grease, you can crumble the bacon and add it to the potatoes after they're cooked through, if desired.
Want to skip bacon grease? You can use vegetable shortening (such as Crisco) or vegetable oil. If you aren't using bacon grease, you'll probably want to add more salt to the potatoes.
If you have leftover baked potatoes, you can dice them up and fry them the same way--you just won't need to fry them as long since they're already cooked.
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