Heat oil in a large pot over medium high heat.
Add sausage, breaking it up with the edge of your spoon, and saute until browned and cooked through, 5 minutes.
Reduce heat to medium low. Add onion and garlic along with a sprinkle of kosher salt and continue sauteing until the onion is soft and lightly browned, 5 minutes more.
Pour in wine. Increase heat to bring to a boil and stir to deglaze. Boil 1-2 minutes or until reduced by half.
Add marinara, stock, oregano, and red pepper flakes. Bring back to a boil, then reduce heat so that everything is at a low simmer. Simmer for 10 minutes.
Add tortellini. Cook until tender (this is 4-5 minutes with my package - check your own for timing).
Take the soup off the heat and stir in pesto. Serve with fresh basil and shredded parmesan.