Easy Spinach, Mushroom and Ricotta Stuffed Zucchini Boats

Ingredients

• 4 medium zucchini, about 2 lb (900 g) total
• 1 tablespoon extra virgin olive oil
• 1/2 teaspoon kosher salt, divided
• 1/4 teaspoon black pepper, divided
• 8 oz (225 g) cremini mushrooms, finely chopped
• 2 cloves garlic, minced
• 1 cup chopped reserved zucchini centers
• 4 cups (120 g) fresh spinach, roughly chopped
• 1 cup (250 g) whole milk ricotta cheese
• 1 large egg, lightly beaten
• 1/3 cup (30 g) grated Parmesan cheese
• 1 tablespoon chopped fresh basil, plus more for serving
• 1/4 teaspoon dried Italian seasoning
• Pinch of red pepper flakes, optional
• 3/4 cup (85 g) shredded mozzarella cheese