Preheat oven to 450 degrees.
Bring a medium pot of salted water to a boil, cook potatoes until tender, about 15-20 minutes; drain well.
Place potatoes onto a baking sheet. Using a potato masher or fork, carefully smash the potatoes until flattened but still in one piece. Drizzle with olive oil and lightly salt. Place into oven and bake for 18-20 minutes, or until golden brown and crisp.
Meanwhile, generously season chicken with sea salt and pepper. Heat 1 tablespoon oil in a large skillet over medium. Place chicken thighs, skin side down, in skillet and sear until skin is browned and crisp, 10–12 minutes. Flip the chicken and continue until cooked through, 8–10 minutes longer. Remove thighs from pan and set aside to rest.
Pour off some of the fat from skillet and increase heat to medium-high. Add shallot and ½ tsp. red pepper flakes and toss to coat. Add escarole in large handfuls, letting it wilt slightly before adding more. Cook until just slightly wilted.
Serve chicken thighs with escarole and smashed potatoes. Squeeze lemon over and top with more red pepper flakes.