Italian Sausage Stuffed Shells

Ingredients

• ✓ 1 (16 ounce) package jumbo pasta shells
• ✓ 3 teaspoons vegetable oil, divided
• ✓ 1 pound bulk Italian sausage
• ✓ 1 (16 ounce) package finely shredded mozzarella cheese, divided
• ✓ 1 teaspoon dried Italian seasoning, plus more for garnish if desired
• ✓ 1 (24 ounce) jar prepared marinara sauce