Heat a large (10 to 12-inch) cast iron skillet over medium-high heat and add the bacon. Cook, stirring frequently, until the bacon has crisped up and much of the fat has rendered, about 5 to 8 minutes. Use a metal spatula to transfer the bacon to a bowl or plate and set aside.

Add the onions to the skillet and cook in the bacon fat until they begin to turn translucent, stirring occasionally, about 3 to 5 minutes. Transfer the onions to the same plate/bowl as the bacon, leaving the bacon drippings behind.

Transfer the sweet potatoes to the skillet and stir very well until the potatoes are coated in bacon fat. Note: if at any point you run out of fat, add 1 to 2 tablespoons of avocado oil to the skillet. Cover the skillet and allow potatoes to cook undisturbed for 5 minutes. Use the metal spatula to stir the potatoes well, then cover the skillet again and cook another 2 to 3 minutes. 

Add the bacon and onions back to the skillet and incorporate them into the potatoes with the spatula.

Add the spinach on top and cover. Cook for 1 to 2 minutes until the spinach becomes easier to stir into the mixture. Uncover the skillet and incorporate the spinach into the hash. Continue cooking until spinach has wilted completely, the potatoes are crispy and cooked through.

Serve the sweet potato hash alongside your favorite omelette, scramble, frittata, and/or breakfast casserole.