Cook the tortellini according to the package directions, drain, and rinse.
Heat the oil in the bottom of the large pot over medium-high heat. Add the garlic, and cook, stirring frequently, until fragrant, about 1 minute, careful not to burn it.
Stir in the tomatoes, spinach, Italian seasoning, salt, and pepper. Cook, stirring occasionally, until the spinach has wilted, about 2 minutes.
Gradually whisk in half and half and Parmesan cheese, stir and cook, whisking constantly, until the sauce is slightly thickened, about 3 to 4 minutes. Add the tortellini to the sauce and gently toss to combine.