Step 1

Place a rack in top third of oven; preheat to 425º. Pat 6 chicken thighs dry with paper towels; season all over with salt.

Step 2

Place a large ovenproof skillet on stovetop and pour in 2 Tbsp. oil. Transfer chicken thighs to skillet, skin side down, and heat over medium. (That's right: Those chicken thighs are going into a cold pan, and then you turn the heat on. Trust!) Cook, rotating skillet to encourage even browning, until opaque around the edges and skin is deeply golden brown, 8–11 minutes. Transfer skin side up to a plate.

Step 3

Meanwhile, do some prep: First, remove fennel fronds from 1 fennel bulb and reserve for making the sauce. Cut fennel head in half lengthwise. Place halves cut side down on cutting board, then cut each half into ½" wedges.

Step 4

Peel and slice 2 shallots into quarters lengthwise.

Step 5

Cut 1 tomato crosswise into ½" rounds.

Step 6

Trims ends off 1 lemon. Cut half of the lemon into thin rounds (about ⅛"). Reserve remaining half of lemon for later.

Step 7

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

Step 8

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

Step 9

Transfer skillet to oven and roast until chicken thighs are cooked through (an instant-read thermometer inserted into thickest part near the bone should register 165°), juices run clear, and vegetables begin to caramelize around edges of pan, 16–20 minutes. Carefully remove skillet from oven and let rest 5 minutes.

Step 10

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

Step 11

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.

Step 12

Spoon fennel oil over chicken and serve with toast alongside.