Creating Stuffed Portobello Caps with Pesto and Mozzarella can easily be achieved by following these clear steps:

1. Preheat your oven to 375°F (190°C) and lightly grease a baking sheet with olive oil.
2. Clean the mushrooms by gently wiping their tops with a damp cloth. Remove the stems and scrape out the gills using a spoon without damaging the caps.
3. Drizzle olive oil over both sides of each mushroom cap. Sprinkle with salt and pepper for seasoning.
4. Spread pesto evenly inside each mushroom cap, filling them generously.
5. Top with mozzarella cheese, ensuring each cap is filled to the brim with melty goodness.
6. Sprinkle grated Parmesan cheese on top for added flavor and a golden finish.
7. Bake in the preheated oven for 20-25 minutes or until the mushrooms are tender and the cheese is bubbly and golden.

These steps will guide you through the straightforward process of creating this deliciously stuffed dish.