Pimentos are most commonly seen as the red portion in the middle of green olives, although they are also available in jars or cans by themselves. Pimento is the Spanish word for pepper, and it refers specifically to highly sweet bell pepper. If you do not have them, you can use diced fresh red bell peppers. Combine them with the onions to soften them. If you wish to add spice to the dish, you can also use a spicier canned pepper.