Prep the eggs: Crack the eggs into a medium bowl, whisk them lightly with a fork until smooth, and set them aside.

Crisp the potatoes: Add the diced potatoes to the skillet in an even layer and cook for 6 to 8 minutes, stirring occasionally, until they are golden brown and tender.

Toast the tortillas: Add the corn tortilla strips to the skillet with the potatoes and cook for 2 to 3 minutes, stirring frequently, until the strips are toasted and crispy.

Warm the beans: Reduce the heat to medium-low, then stir in the drained black beans, ground cumin, and kosher salt to warm them through.

Wilt the spinach: Add the fresh baby spinach to the skillet and toss for about 1 minute until the leaves are just wilted.

Add the eggs: Pour the whisked eggs directly into the skillet over the potato, bean, and tortilla mixture.

Scramble the migas: Gently push and fold the eggs around the skillet with a spatula for 2 to 3 minutes, stopping when the eggs are just set but still soft and slightly runny.

Finish and serve: Remove the skillet from the heat immediately and serve the migas warm, topped with crumbled cotija cheese if using.