Prep the vegetables and chicken: Cut everything into evenly sized pieces so they cook at the same rate.
Pat the chicken dry and season with a pinch of salt and pepper.
Build flavor: In a skillet over medium heat, warm the olive oil or butter. Sauté the onion and celery for 4–5 minutes until softened. Stir in the garlic and tomato paste and cook 1 minute until fragrant.
This step adds rich flavor to the stew.
Load the slow cooker: Add carrots, potatoes, green beans, sautéed aromatics, drained tomatoes, chicken, thyme, rosemary, bay leaf, Worcestershire sauce, salt, and pepper to the slow cooker. Pour in the chicken broth.
Set and cook: Cover and cook on Low for 6–8 hours or High for 3–4 hours, until the chicken is tender and the vegetables are cooked through.
Thicken (optional): In the last 20 minutes, stir in the cornstarch slurry. Add the frozen peas.
Cover and let it simmer until slightly thickened and the peas are heated through.
Finish and season: Remove the bay leaf. Taste and adjust salt and pepper. Stir in chopped parsley for freshness.
Serve: Ladle into bowls and serve with crusty bread for dipping.
The broth is savory and rich, so bread is a nice touch.