Bring a large pot of water to boil. Add tortellini and cook according to the package instructions. Drain.
Slice skinless, boneless chicken thighs into thin strips. Season generously with smoked paprika, salt, and freshly ground black pepper.
Heat an empty large cast-iron skillet over medium heat for 3 minutes. This allows the cast-iron skillet to heat through. Add 2 tablespoons of olive oil. Add sliced chicken thighs in a single layer, without overcrowding. You might have to work in batches. Cook the chicken on medium heat for 4 minutes, without moving it at all so that it sears nicely.
Flip the chicken slices over, reduce heat to low-medium, and cook for about 5 more minutes or longer until it's cooked through. Remove the chicken from the skillet to a plate.
To the same, now empty, cast-iron skillet, add butter and minced garlic. Cook on low-medium heat for about 1 or 2 minutes or until the garlic softens.
Add cooked tortellini and coat thoroughly with the garlic butter sauce on low-medium heat.
Add back cooked chicken and stir to coat the chicken with the garlic butter sauce on low-medium heat. Remove from heat.
Add roasted butternut squash and roasted Brussels sprouts to the skillet with cooked chicken and cooked tortellini. If you used a large skillet, everything should fit. If not, work in batches. Top with fresh thyme. Season with salt and freshly ground black pepper to taste.