Cube the beets and potatoes (1/2-inch pieces), keeping them separate. Put them in separate saucepans with water to cover and bring to a boil. Boil until tender, about 5 minutes for the potatoes and 15 minutes for the beets. Drain well and place both in one big bowl.
If you are using bacon, fry it in a large skillet until crispy, then drain well and crumble or chop it inti small bits. Add the bacon bits to the beet mixture and discard the bacon fat.
In the same skillet, heat half the oil and saute the onion until browned. Stir the browned onion into the beet mixture and season the mixture with salt and pepper.
Add the rest of the oil to the skilet. Spread the beet-potato mixture evenly in the skillet and saute iver medium heat without strring, until the poatoes are crisp and brown on the bottom. Use spatula to turn the hash; browned again repeat until most of the potatoes are browned. Season with more salt and pepper if needed, and serve hot.