1 pound cod fillet (see Ingredient note)
3 teaspoons extra-virgin olive oil, divided
1/4 teaspoon freshly ground pepper
1 tablespoon minced shallot
1 cup halved cherry tomatoes
1/4 cup chopped cured olives
1 tablespoon capers rinsed and chopped
1 1/2 teaspoons chopped fresh oregano
1 teaspoon balsamic vinegar