Heat oil in a large cast iron or non-stick skillet over medium heat.
Beat the eggs together in a large bowl. Whisk in the milk, cumin, and chili powder. Add the grated cheese and the ribboned spinach; stir to combine.
Once the oil in the pan is hot, pour the egg mixture into it. Bring the heat to medium-low. (You don't want to rush cooking the eggs or they'll become rubbery.) Once the eggs hit the pan, they will begin to cook immediately. With a spatula, pull the cooked outer edges in towards the center of the eggs, creating soft and silky curdles. Any uncooked egg mixture will flood toward the outer edges of the pan. Keep pulling the outer cooked edges into the center with your spatula. Eventually, the uncooked eggs will stop flooding the outer edges of the pan and all of your eggs will be curdled in the center of the pan. At this point you can start breaking up the scrambled eggs. Turn any undercooked eggs and keep the scramble moving to make sure the eggs cook evenly. (Never thought explaining scrambling eggs would be this involved… )
Once the cheesy spinach-filled egg scramble is cooked, spoon the egg mixture into taco shells. Top them with black beans, and whatever else you fancy. We like to add juicy diced tomatoes, creamy avocado, tangy pico de gallo, and a drizzle of hot sauce. Oh, and extra cheese, of course. A nice squeeze of fresh lime juice brightens things up as well.
Serve the tacos while the eggs are warm. These tacos are perfect for breakfast or brunch, but they're also incredible for those nights where you're hankering breakfast for dinner!