In a medium skillet over medium-high heat, add the sun-dried tomatoes with any excess oil, and minced mushroom stems. Add 1-2 more teaspoons of olive oil, seasoning with salt and pepper. Cook until softened and fragrant, 3-4 minutes. Remove from heat and set aside.
Preheat oven to 375 degrees F.
In a medium mixing bowl, combine the tuna, mayonnaise, 3/4 c Parmesan, Dijon, lemon zest, and sun-dried tomato mixture. Mix until combined, season with additional pepper if needed.
Brush the mushroom caps with olive oil all over and arrange on a parchment-lined tray. Fill all caps with the tuna and sprinkle with remaining Parmesan, making sure the large caps are near the edges of the tray and the smaller in the center to encourage more even cooking.
Bake for 15 minutes, or until browned on top. Serve warm, garnished with basil, drizzled with olive oil, and seasoned with salt and pepper.
Notes
Clean mushrooms with a damp paper towel, don’t rinse
Garnish with other herbs like cilantro or mint
Use canned tuna
Add some spice by adding chili flakes to the sun-dried tomatoes and mushroom stems as they cook