Remove the chicken pieces from the marinade mixture, shaking off excess onion, bell pepper and/or scallion bits; do not discard the marinade; set aside.
Set the chicken aside on a medium baking sheet or large plate or platter.
In a large heavy-bottomed pot or Dutch oven, over medium-high heat, heat the oil.
Once the oil is shimmering, gently swirl the pot around to evenly coat the bottom.
Add a few chicken pieces into the pot, working in batches, careful not to overcrowd.
Sear the chicken on all sides until a deep brown crust appears; about 2 to 3 minutes on each side.
Transfer the browned chicken onto a clean, medium baking sheet or large plate or platter and repeat the process until all the chicken pieces are browned; add a little more of oil in between batches, as needed.
Set the browned chicken aside and reduce the heat to medium.