Preheat the oven to 350°F (175°C) and grease a 9x13 baking dish.
On a plastic cutting board, trim any visible fat from the chicken livers and slice the larger ones into smaller pieces for even cooking. Gently pat them dry with a paper towel to absorb excess moisture. Wash your hands well after handling the livers.
Place the sliced onions at the bottom of the greased baking dish. Place the cleaned chicken livers on top of the onions. Drizzle the olive oil over the top. Season everything with salt, garlic powder, onion powder, paprika, and oregano (or Italian seasoning). Using your hands or kitchen tongs, toss to season both the onions and chicken livers with the olive oil and seasonings.
Cover the baking dish with foil.
Bake:
Bake, covered, in the preheated oven for a total of 30 to 35 minutes. Open the oven after 20 minutes, remove the foil cover, and stir the livers and onions. Continue cooking for the remaining 10 to 15 minutes until the chicken livers are cooked through but still look tender. When poking them with a meat thermometer, the internal temperature reaches 165F.
Remove from the oven and serve.
Notes
For a milder flavor, you can soak the chicken livers in milk for about an hour before cooking. This step is optional and based on personal preference.