Mix flour, chipotle chili powder, garlic powder, cinnamon, coriander, salt, and black pepper in a large resealable plastic bag and shake to combine. Place the turkey breast into the bag, seal, and shake to coat turkey with the spice mix.
Heat olive oil in a large skillet over medium heat and sear the seasoned turkey breast in the hot oil until browned on both sides, about 5 minutes per side (meat will still be pink inside).
Place acorn squash quarters, carrots, red onions, and garlic cloves into the bottom of a large slow cooker. Place the browned turkey breast on top of the vegetables. Cover cooker.
Cook turkey breast until meat and vegetables are very tender, 3 1/2 to 4 hours on High or 7 to 8 hours on Low. Transfer turkey breast to a platter and allow to rest for about 10 minutes before slicing.
Peel squash and garlic cloves. Arrange the cooked vegetables around the turkey meat and spoon the juices from the slow cooker over the turkey and vegetables to serve.