Swordfish With Sweet and Hot Peppers

Name: Swordfish With Sweet and Hot Peppers
Ingredients: 2 tablespoons extra-virgin olive oil; 1 small white onion, thinly sliced; 4 cups sliced sweet peppers (a mix of bell peppers, cubanelle and others, as many colors as possible); 1 tablespoon chopped fresh oregano; 1 1/4 teaspoon salt; 1/2 teaspoon black pepper; 3 tablespoons unsalted butter; 1 1/2 pounds swordfish, skin removed, cut into 1 1/4-inch chunks; 2 to 3 fresh chile de arbol or other hot chile peppers, seeded if desired, and thinly sliced; 1 garlic clove, minced; Lemon juice, as needed; Chopped cilantro, as needed