Apple Cheddar Quesadilla

1/4 cup chopped onions

3 tsp. vegetable oil, divided

1/2 tsp. kosher salt, divided

2 (8-Inch) tortillas

1 apple, thinly sliced

1/2 cup (2 oz.) Sargento® Shredded Mild Cheddar Cheese - Fine Cut

1/4 cup (1 oz.) Sargento® Shredded Mozzarella - Fine Cut