Cook rice according to package directions and set aside.

In a small bowl, whisk together onion soup mix, 1¼ cups water, and 1 Tbsp Worcestershire sauce.

In another bowl, mix 1 Tbsp cornstarch with 1 Tbsp cold water until smooth; set aside.

Cut 1 lb chicken into bite-sized pieces. Heat 1 Tbsp butter in a skillet, add chicken, and brown for 1–2 minutes per side. Remove chicken to a plate.

In the same skillet, sauté ½ cup onion, ½ cup green pepper, and 1 can mushrooms for 2–3 minutes, until softened.

Stir in the onion soup mixture, then add the chicken back in. Reduce heat, cover, and cook 8–10 minutes, until chicken is cooked through.

Remove chicken to a bowl. Pour the cornstarch mixture into the skillet and bring to a gentle boil. Stir for 1–2 minutes, until thickened.

Pour sauce over chicken and serve with rice.