Heat olive oil in a large skillet or sauté pan over medium heat. Add onions and sauté until they begin to get translucent, about 3 minutes; then add garlic. Cook garlic just until it becomes fragrant, about 30 seconds, then add tomato paste. Cook for about a minute, stirring frequently to prevent it from burning. Next, add beans and stir into the mixture; then add tomatoes, any liquid and water. Add oregano, salt and pepper. Mix everything to incorporate. If the mixture is a bit dry, add more water a tablespoon at a time. Reduce heat, cover and let the beans stew in the tomato sauce for 15-20 minutes. Beans should be cooked until very tender.