Heat 1 teaspoon of olive oil in a medium skillet over medium heat. Add finely chopped onion and sauté until translucent and slightly golden, about 4-5 minutes.
In a mixing bowl, combine cooked chicken, sautéed onions, 2 tablespoons breadcrumbs, ground sage, salt, and pepper. Mix well.
Shape the chicken mixture into oval or round croquettes, about the size of a golf ball.
In a shallow dish, beat the egg. In another shallow dish, place the remaining breadcrumbs.
Dip each croquette into the beaten egg, then roll it in the panko breadcrumbs until fully coated.
Heat enough oil in a frying pan to submerge the croquettes. Fry them in batches until golden brown and crispy, about 3-4 minutes per side.
Remove croquettes from the oil and place them on paper towels to absorb excess oil. Serve warm.
