Preheat the oven to 375°F.
Season the chicken with salt, pepper, paprika, and garlic powder..
Heat olive oil in a 12-inch cast-iron skillet over medium-high. Sear the chicken for 3 to 4 minutes per side until golden. Transfer to a plate and set aside (it will finish in the oven).
Reduce heat to medium, add the garlic and cook for 30 seconds. Stir in the sun-dried tomatoes, Dijon, and chicken broth, scraping up any browned bits.
Add the spinach and cook until just wilted, then season with the remaining salt and pepper.
Stir in the milk and bring to a gentle simmer.
Add in the tortellini and toss to coat.
Nestle the chicken back into the skillet, top with parmesan, and bake uncovered until the chicken is cooked through and the tortellini is tender, about 15 minutes.
Remove from the oven, rest 5 minutes, garnish with basil, and serve.