Preheat oven to 400F.
Add water to a large pot over medium-high heat; once the water starts to boil, cook the tortellini by following the recommended time on the package, usually 5-7 minutes. Cook for 1-2 minutes less than the recommended time. Drain and return the tortellini to the pot. Add the pesto and stir gently until combined.
In the meantime, place a large skillet over medium heat and add two tablespoons of olive oil.
Slice the sausages and add them to the hot skillet. Cook for 2-3 minutes, stirring often, until the sausages start to brown. Remove the skillet from heat and set aside.
Add the browned sausages, tomatoes, spinach, and cheese to the pot with the tortellini. Stir well but gently so as not to crush the tomatoes or the tortellini. Save a little cheese, about 1 cup, to top the casserole.
Add a little olive oil, about one tablespoon, to a 9-inch casserole dish. Add the tortellini mixture to the casserole, top with the remaining cheese, and bake for 20-25 minutes until the top layer looks golden—light brown.
Serve and enjoy.
