Carefully clean each mushroom by gently wiping them with a damp cloth to remove dirt. Remove the stems and set them aside, as they will not be used in the filling.
In a large skillet over medium heat, add a drizzle of olive oil. Once hot, add the finely chopped onion and minced garlic. Sauté for about 3–4 minutes, or until fragrant and the onion becomes translucent.
Increase the heat slightly and add the ground beef to the skillet. Use a spatula to break the beef into crumbles. Cook for approximately 5–7 minutes, or until the meat is fully browned and cooked through.
Once the beef is browned, stir in the Worcestershire sauce, along with a pinch of salt and pepper to taste. Mix well and continue to cook for an additional minute to allow the flavors to meld together.
Remove the skillet from the heat and let the mixture cool for a couple of minutes. Then, add the breadcrumbs, half of the shredded cheddar cheese, and the chopped fresh parsley. Stir until everything is well combined.
Generously spoon the beef mixture into each mushroom cap, ensuring to mound it slightly for an appetizing look.
Arrange the filled mushrooms on a baking sheet lined with parchment paper. Sprinkle the tops of each mushroom mound with the remaining cheddar cheese.
Lightly drizzle some olive oil over the stuffed mushrooms to enhance their cooking and provide a golden finish.
Bake in the preheated oven for 20–25 minutes, or until the mushrooms are tender and the cheese is melted, bubbly, and golden brown.
Once done, remove the baking sheet from the oven and allow the mushrooms to cool for a few minutes before serving.
Notes
Serve on a decorative platter, garnished with extra chopped parsley. Consider using toothpicks for easy picking.