In a medium-sized saucepan, heat the marinara sauce over medium heat until it starts to simmer.
Add the frozen meatballs, cover and let simmer over medium-low heat for 15 minutes, stirring occasionally.
Fill a large pot with 4-6 quarts of water and bring to a boil. Once the water is boiling, add 2 teaspoons of olive oil, and then add the jumbo pasta shells.
Cook the jumbo pasta shells for 9 minutes, drain and let them cool for a few minutes.
Preheat the oven to 400F. Line a large rimmed baking sheet with parchment paper. Spread 20 of the cooked and cooled pasta shells out evenly on the parchment-lined baking sheet.
Fill each shell with 1 teaspoon of cheese, 1 marinara simmered meatball, a teaspoon of marinara sauce from the saucepan, and another teaspoon of cheese on top. Place the filled pasta shell back on the baking sheet. Repeat process until all meatballs have been stuffed into a pasta shell.
Bake for about 5 minutes or until cheese on top of each stuffed pasta shell is melted.