1. The night before, or 1 hour before making tacos soak potatoes in a bowl of cold water and place them in the fridge. This will remove any excess starch resulting in extra crispy potatoes.
2. Preheat a large cast iron skillet over medium heat. Drain potatoes and blot excess water with a paper towel.
3. Heat vegetable oil in cast iron and carefully add potatoes to the pan. Spread in an even layer and cook undisturbed for about 5 minutes. Stir potatoes and cook for another 3 minutes—season with salt and fajita seasoning. Stir to coat and cook for another 4-5 minutes until crispy.
4. Move potatoes to one side of the cast iron skillet. Add a little bit more vegetable oil to the pan. Add SPAM and spread in an even layer. Cook undisturbed for about 3 minutes. Stir SPAM and cook for another 2-3 minutes until crispy.
5. While the SPAM is cooking, heat a medium cast iron skillet over medium heat and warm flour tortillas on both sides. Keep warm in aluminum foil.
6. Turn off the burner with SPAM and potatoes and keep warm.
7. In the same pan, you cooked the tortillas in, turn the heat to low. Add butter and allow the butter to melt. Add scrambled eggs. Cook eggs by moving the eggs around with a rubber heat proof spatula until cooked through. Remove from heat.
8. To assemble the tacos, add cheese to the warm tortilla, top with egg, potato, and SPAM, and top with restaurant-style salsa or your favorite hot sauce.