Preheat oven to 400°F. Place tortillas on a baking sheet and toast in the oven for about 10 minutes, flipping once, until they are crispy and golden.
Heat beans in a small saucepan over medium heat, or heat in the microwave, covered, until warmed through.
In a small saucepan, heat enchilada sauce over medium low heat.
Spray a large nonstick skillet with cooking spray or grease with a little bit of olive oil. Heat skillet to medium heat. Crack eggs, one at a time into pan and cook until whites are done and yolks are slightly runny.
To assemble tostadas, spread black beans over each tortilla. Top each with an egg, 1-2 tbsp of sauce, and garnish as desired with cilantro, queso fresco, jalapeño or avocado slice.