Combine the diced tomatoes, onion, cilantro, lime juice, and salt to make the pico de gallo. Adjust the lime, cilantro, and salt to taste.
Stir the chili powder, garlic powder, cumin, and cayenne into the refried beans.
Preheat the oven to 400°F. Spread the seasoned beans over the tostada shells, place them on a lined baking sheet, and bake for 3 to 5 minutes until crisp and hot.
While the tostadas bake, fry or scramble the eggs and season them with salt and black pepper.
Top each hot tostada with an egg, pico de gallo, and optional grated cheese. Serve immediately.
Notes
Assemble immediately before serving so the tostada shells remain crisp.