In a skillet over medium heat, add the olive oil. Once hot, sauté the diced onion until translucent, about 5 minutes. Add the minced garlic and cook for another minute until fragrant.
Season the chicken breasts generously with salt, pepper, paprika, thyme, and rosemary on both sides.
Place the seasoned chicken breasts in the slow cooker. Pour the sautéed onion and garlic mixture over the chicken, ensuring it’s evenly distributed.
Pour the chicken broth and heavy cream over the chicken, covering it well.
Cover the slow cooker and set it on low for 6-7 hours or high for 3-4 hours, until the chicken is tender and cooked through.
About 30 minutes before serving, stir in the baby spinach and cover again to let it wilt.
Remove the chicken from the slow cooker and shred it using two forks, if desired. Mix the shredded chicken back into the creamy sauce or serve the chicken whole with sauce spooned over it.