Crock Pot Colorful Chicken Stew

1 (14 1/2 ounce) can Italian-style diced tomatoes , undrained

2 medium potatoes , peeled and cut into 1/2 " cubes

5 medium carrots , chopped

3 celery ribs , chopped

1 large onion , chopped

1 medium green bell pepper , chopped

2 (4 ounce) cans mushroom stems and pieces , drained

2 low-sodium chicken bouillon cubes

artificial sweetener , equal to 2 tsp. sugar

1 teaspoon chili powder

1/4 teaspoon pepper

1 tablespoon cornstarch

2 cups cold water