Preheat oven to 425°F (220°C). Wipe portobello caps with a damp cloth, remove stems and gently scrape out gills with a spoon if desired to reduce moisture and create more room for filling.

Place the mushrooms gill-side up on a baking sheet lined with parchment. Brush both sides lightly with 2 tbs olive oil and season each cap evenly with 1 tsp salt and 1 tsp freshly ground black pepper.

Make herb-garlic filling

In a medium skillet, heat 2 tbs butter and 1 tbs olive oil over medium heat until butter melts and begins to sizzle gently.

Add the minced garlic and diced shallot. Sauté for 1.5–2 minutes until fragrant and softened but not browned.

Stir in chopped parsley, thyme leaves, lemon zest, 1 tsp salt, 1/2 tsp black pepper and 1 tsp red pepper flakes. Cook for another 30–45 seconds to bloom the herbs and spices. Remove from heat.

If you prefer a spreadable filling, finely chop the mixture or pulse briefly in a small food processor; otherwise leave as-is for a chunkier texture.

Assemble with cheese and topping

Spoon or press the warm herb-garlic mixture into each mushroom cap, distributing evenly (about 2 tbs filling per cap).

Top each stuffed cap with roughly 2 oz (about 1/2 cup total per two caps) of fresh mozzarella pieces so the cheese covers the filling.

Combine the panko (0.25 cups) with 1 tsp olive oil and a pinch of salt; sprinkle a thin layer of the panko over the cheese, then grate or sprinkle about 1 tbsp Parmesan over each cap (use remaining Parmesan to taste). The panko is optional but gives a crisp finish.

Bake and finish

Bake in the preheated oven for 12–15 minutes, until the mushrooms are tender, the cheese has melted and the panko is golden. If you want more browning on the cheese, switch the oven to broil for 1–2 minutes — watch closely to prevent burning.

Remove from oven and let rest 2–3 minutes. Drizzle each cap with about 1/2 tbs balsamic glaze (total 2 tbs for 4 caps). Sprinkle with chopped parsley for color and an extra crack of black pepper.

Serve warm with lemon wedges on the side for a squeeze of brightness.