Season the chicken: Pat the chicken dry. Season with 1 teaspoon salt, 1/2 teaspoon black pepper, and half the dried thyme or Italian seasoning.
Sear in a hot pan: Heat olive oil in a large skillet over medium-high.
Add chicken in a single layer. Cook 3–4 minutes per side until browned and mostly cooked. Transfer to a plate.
Sauté aromatics: Reduce heat to medium.
Add onion and a pinch of salt. Cook 3–4 minutes until soft. Stir in garlic and red pepper flakes, cooking 30 seconds until fragrant.
Deglaze and build the sauce: Pour in chicken broth and scrape the pan to release browned bits.
Stir in Dijon, remaining dried herbs, and lemon juice.
Add peas: Stir in peas. Simmer 2–3 minutes (fresh may need a bit longer) until bright and tender.
Return chicken: Add the chicken and any juices to the pan. Simmer 3–5 minutes until the chicken is cooked through and the sauce slightly reduces.
Finish: Stir in butter for a glossy finish (optional).
Taste and adjust with more salt, pepper, or lemon juice. Fold in parsley or dill.
Serve: Spoon over rice, couscous, or quinoa, or serve with crusty bread to catch the sauce.