Our Best Stuffed Mushrooms

Name: Our Best Stuffed Mushrooms
Ingredients: 1 pound cremini mushrooms (about 24), stems removed and finely chopped; 4 tablespoon extra-virgin olive oil, divided; 1 teaspoon kosher salt, divided, plus more to taste; 1 teaspoon freshly ground black pepper, divided, plus more to taste; 1/4 cup panko breadcrumbs; 2 garlic cloves, minced; 1/4 cup grated Parmesan cheese; 3 tablespoon fresh parsley, roughly chopped, divided; 2 teaspoon finely grated lemon zest; 3 tablespoon freshly squeezed lemon juice (from about 1 lemon); 1/8 teaspoon red pepper flakes (optional)