Gently clean the portabella mushrooms with a damp cloth and remove the gills using a spoon. Place them cap-side up on a lined baking sheet.

Preheat your oven to 375°F (190°C).

In a mixing bowl, combine the breadcrumbs, shredded manchego cheese, garlic powder, chopped scallions, melted butter, milk, salt, and pepper. Mix thoroughly to achieve a cohesive filling.

Drizzle olive oil over the tops of each mushroom cap and season both sides with salt and pepper. Flip the mushrooms cap-side down on the baking sheet.

Spoon the prepared filling into each mushroom cap, creating a well in the center for the egg. Pack lightly to ensure filling stays in place.

Bake the filled mushrooms in the preheated oven for about 10 minutes.

Remove mushrooms from the oven, create an indentation in the center of each filling, and crack an egg into the well. Season with salt and pepper before returning to the oven.

Bake for an additional 10-15 minutes until the egg whites are set but still slightly jiggly.

Let the mushrooms cool for a few minutes and serve warm, optionally with a fresh salad.