Best Jambalaya

Name: Best Jambalaya
Ingredients: 1 tbsp. extra-virgin olive oil; 1 yellow onion, chopped; 2 bell peppers, seeds and ribs removed, chopped; 1 lb. boneless, skinless chicken breasts, cut into 1 pieces; 1 tsp. dried oregano; 6 oz. andouille sausage, sliced; 2 tbsp. tomato paste; 2 cloves garlic, finely chopped; 2 c. low-sodium chicken stock; 1 (15-oz.) can crushed tomatoes; 1 c. long-grain rice; 2 tsp. Old Bay seasoning; 1 lb. medium shrimp, peeled, deveined; 2 scallions, thinly sliced