Preheat oven to 400°. Pull the stems off the portobellos and put them in a baking dish, top sides down. Spread 1 tablespoon of tomato sauce on each mushroom then break an egg over top and bake for 20-25 minutes, until the eggs are set.
Recipe by Love from the Land at https://www.lovefromtheland.com/portobello-egg-cups/