Step 1:

• Preheat the oven to 375°F (190°C).
• Line a baking sheet with parchment paper or lightly grease it with olive oil.

Step 2:

• In a skillet, heat the olive oil over medium heat.
• Add the chopped onion and minced garlic, and sauté until softened, about 3-4 minutes.

Step 3:

• Add the breadcrumbs to the skillet and toast them until golden brown, about 2-3 minutes.
• Remove from heat and let cool slightly.

Step 4:

• In a mixing bowl, combine the toasted breadcrumb mixture with grated Parmesan cheese, chopped parsley, salt, and pepper.
• Mix well to combine.

Step 5:

• Stuff each mushroom cap with the breadcrumb mixture, pressing gently to pack it in.

Step 6:

• Arrange the stuffed mushrooms on the prepared baking sheet.
• Pour vegetable broth or water into the bottom of the baking sheet to prevent the mushrooms from drying out.

Step 7:

• Bake in the preheated oven for 20-25 minutes, or until the mushrooms are tender and the filling is golden brown.