Preheat your oven to 400°F (200°C).
Place the corn tortillas directly on the oven rack or a baking sheet and bake for 4-5 minutes per side until they are golden brown and crisp.
While the tortillas bake, rinse and drain the black beans, then place them in a small saucepan over medium heat with a tablespoon of water to warm through.
In a medium mixing bowl, whisk together the large egg and egg whites until the mixture is uniform.
Heat a non-stick skillet over medium-low heat. Pour in the egg mixture and cook, stirring frequently with a spatula, until the eggs are fluffy and just set.
Season the cooked eggs with sea salt and black pepper.
To assemble, divide the warm black beans evenly between the two crispy tortillas, spreading them into a thin layer.
Top the beans with the scrambled eggs, followed by a dollop of Greek yogurt on each.
Finish the tostadas by sprinkling with crumbled feta cheese, salsa, and fresh cilantro before serving immediately.