Preheat the oven to 475˚F (245˚C). Line a large sheet pan with parchment paper or foil (if using foil, rub it lightly with oil or spritz it with cooking spray).
In a large bowl, combine the onion, fennel, kale and garlic cloves. Using a microplane, zest the lemon and add the zest to the bowl. Thinly slice the lemon into rings and pop out the seeds. Add the lemon slices to the bowl, and drizzle in 2 tablespoons of the olive oil. Season with salt and pepper, and toss well to coat. Spread the vegetables on the prepared sheet pan. Arrange the torn baguette pieces evenly over top.
In the same bowl you used for the vegetables (no need to wash it), add the chicken thighs, oregano, paprika, and 1 tablespoon of olive oil. Season with salt and pepper, and toss well to coat the chicken. Arrange the chicken, skin side up, on top of the vegetables and bread on the sheet pan.
Roast the chicken for 15 minutes. Transfer the chicken to a plate (it won’t be fully cooked yet). Gently stir the vegetables and bread on the baking sheet. Rearrange the chicken on top, positioning any darkened pieces of bread under the chicken. Roast 12-15 minutes longer, or until the juices run clear and the internal temperature reads 165-170˚F (70-75˚C).
Transfer the chicken to a clean plate. If you’re using a gluten-free baguette, slide the pan back in the oven for 2-4 minutes to crisp up the bread (there’s no need to do this if using a regular baguette, as it holds up better). Pick the garlic cloves off the sheet pan, and squeeze them into a mini food processor or small blender (alternatively, if the garlic cloves are soft enough and/or if you’re feeling lazy, mash them up with a fork). Add the apple cider vinegar and maple syrup, and season with salt and pepper. Process until smooth. Add the remaining 4 tablespoons of olive oil and process again until incorporated.
Scrape the vegetables and bread into a large bowl, and drizzle with about half of the dressing. Toss to coat, and season with salt and pepper to taste (feel free to add more dressing if you think it needs it). Spoon the salad into shallow bowls or onto plates. Arrange 1-2 pieces of chicken on top, and drizzle with a bit more dressing. Serve any additional dressing at the table.