Put a rack in top third of oven; preheat to 220C/425F.

Using paper towels, pat the chicken thighs dry using paper towels; and season all over with salt.

Place a large ovenproof skillet (or transfer food to Baking Dish before placing in oven) on the stovetop and pour in 2 Tbsp. oil.

Transfer chicken thighs to skillet, skin side down, and heat over medium. (Do Not heat the pan first) Whilst cooking, turning the pan frequently to ensure even browning until they are opaque around the edges and skin is deeply golden brown, 7–12 minutes. Transfer skin side up to a plate.

Whilst cooking, remove fennel fronds from fennel bulb and reserve for making the Fennel Oil..

Cut fennel head in half lengthwise. Place halves cut side down on cutting board, then cut each half into ½" wedges

Peel and slice shallots into quarters lengthwise.

Cut tomato crosswise into ½" rounds.

Cut the ends off the lemon and cut in half, cut one half into thin rounds (about ⅛"). Reserve remaining half of lemon for later.

Adjust the heat under the pan to medium-high and add sliced fennel, shallots, and lemon rounds Cook for 3-4 minutes, stirring occasionally, until fennel just begins to soften. Season with salt and pepper and give mixture another stir. Remove pan from heat.

Arrange tomato rounds and chicken over fennel mixture; season with salt and pepper.

Transfer to an oven-proof dish if not using an appropriate skilet, and place in the oven and roast until chicken thighs are cooked through, 16–20 minutes (an instant-read thermometer inserted into thickest part do not touch the bone temperature should be 80C /165F, make sure that the juices run clear, and vegetables begin to caramelize around edges of pan,. Carefully remove from oven and let rest 5 minutes.

While chicken is roasting, finely chop reserved fennel fronds until you have about ¼ cup..

Squeeze juice from reserved lemon half into a small bowl. Add chopped fronds to bowl and stir in remaining ¼ cup oil; season with salt and pepper.

Spoon the fennel oil over chicken and serve with toasted baguette slices.