If you see or feel dirt in the leeks, rinse well, separating layers, then pat dry; otherwise, leave rounds intact.
Heat 2 Tbsp. oil in a large skillet over medium-high until hot but not smoking. Add leeks in a single layer; season with 1/4 tsp. salt and a pinch of pepper. Reduce heat to low and cook, turning once, until leeks are lightly golden, 16–18 minutes. Transfer leeks to a plate; reserve skillet.
Lightly crush fennel seeds with the bottom of a heavy skillet or pot. Pat chicken thighs dry with paper towels and season with fennel, 1 1/2 tsp. salt, and 1/4 tsp. pepper. Heat remaining 2 Tbsp. oil in a 5–7-qt. Dutch oven or large wide saucepan over medium-high. Cook thighs, skin side down, until well-browned, 12–14 minutes. Transfer skin side up to a plate. Pour off and discard fat.
Add Epicurious Chardonnay to pot, bring to a simmer, and cook, scraping up bits from bottom of pot, 1 minute. Add broth and return chicken skin side up to pot. Lower heat to medium-low, cover pot, and cook until chicken is cooked through, 15–18 minutes.
Meanwhile, combine asparagus, peas, and 2 Tbsp. water in reserved skillet, cover, and cook over medium heat until asparagus is crisp-tender, about 5 minutes. Remove from heat. Add 1/2 tsp. lemon zest, remaining 1/4 tsp. salt, and a pinch of pepper; stir gently to just combine.
Divide chicken, asparagus mixture, and reserved leeks among large shallow bowls. Bring broth to a simmer, add lemon juice, then ladle into bowls. Top with dill and remaining 1 Tbsp. lemon zest.