Stir together lemon rind, juice, and saffron in a small bowl; set aside. Heat oil in a 13- to 15-inch paella pan or skillet with lid over medium-high. Sprinkle chicken with black pepper and 3/4 teaspoon salt. Add 4 chicken thighs to pan; cook, skin side down, until golden brown, about 6 minutes. Turn chicken over; cook until browned, about 3 minutes. Transfer chicken to a plate; repeat with remaining 4 chicken thighs. Add onion, thyme, and garlic to pan; cook, stirring often, 4 minutes. Add rice; cook, stirring often, 2 minutes. Add wine; cook until reduced by about half, about 2 minutes. Stir in lemon juice mixture, stock, and remaining 3/4 teaspoon salt. Nestle chicken, skin side up, into rice. Cover and reduce heat to medium; simmer until rice is just al dente, about 18 minutes. Uncover pan. Add peas and red pepper pieces. Increase heat to medium-high; cook until rice begins to brown on the bottom and edges of pan, about 5 minutes. Remove from heat. Sprinkle with parsley; serve with lemon wedges.