Creamy Ricotta Beef Stuffed Shells Pasta

Ingredients

• 20 -25 jumbo pasta shells
• 1 tablespoon olive oil
• 1 pound ground beef
• 1 medium onion, chopped
• 3 cloves garlic, minced
• 1 teaspoon salt
• 1/2 teaspoon black pepper
• 1/2 teaspoon dried oregano
• 1/4 teaspoon red pepper flakes
• 1 cup ricotta cheese
• 1 cup shredded mozzarella cheese, divided
• 1/2 cup grated Parmesan cheese, divided
• 1 large egg
• 2 cups marinara sauce
• Fresh basil leaves, for garnish (optional)