Bacalao Guisado (Puerto Rican Fish Stew)

Name: Bacalao Guisado (Puerto Rican Fish Stew)
Cook time: 45 min
Total time: 45 min
Cuisine: American
Ingredients: 2 tablespoons extra-virgin olive oil; 1 medium onion, chopped; 4 cloves garlic, minced; 1 pound flaky white fish, such as haddock, tilapia or cod (see Tip), cut into 1 1/2-inch pieces; 1 14-ounce can diced tomatoes; 1 Anaheim or poblano chile pepper, chopped; 0.25 cup packed chopped fresh cilantro; 2 tablespoons sliced pimento-stuffed green olives; 1 tablespoon capers, rinsed; 1 teaspoon dried oregano; 0.5 teaspoon salt; 0.5 cup water, as needed; 1 avocado, chopped (optional)