Season the chicken thighs with salt, pepper, thyme, and rosemary, rubbing in the herbs and spices thoroughly.
Heat the olive oil in a large skillet over medium-high heat until shimmering. Sear the chicken thighs, skin side down, until golden brown and crispy, about 4-5 minutes. Flip and sear the other side for an additional 3 minutes.
Remove the chicken from the skillet and set aside. Toss the chopped vegetables into the same skillet, stirring briefly to coat with the flavorful oil and juices. Cook until they start to caramelize around the edges, about 8 minutes, and then transfer everything to your slow cooker.
Add the minced garlic and lemon zest to the skillet; cook for 30 seconds until fragrant, scraping up any browned bits from the bottom. Pour the chicken broth into the skillet, bringing it to a simmer to deglaze, then pour this mixture over the vegetables in the slow cooker.
Arrange the seared chicken thighs on top of the vegetables in the slow cooker. Cover with the lid, set to low, and cook for 4 hours until the chicken is fall-off-the-bone tender and the vegetables are soft and caramelized.
Once cooking is complete, gently remove the chicken and vegetables. Serve the chicken with the fragrant vegetables on the side, garnished with fresh thyme sprigs for a pop of color and flavor.