Season the chicken chunks with salt and pepper. In a large pot or deep skillet, heat the tablespoon of oil over high heat. Add the chicken pieces in a single layer and sear them for about 5 to 6 minutes per side, or until golden brown. The more color they get, the better the flavor of the stew.

Remove the chicken and set it aside. In the same pot, reduce the heat to medium and add the diced onion. Cook for 3 to 4 minutes until soft and translucent. Add the diced fresh tomatoes and stir well. Cook for about 2 minutes so they start to soften and release their juices. At this point, return the browned chicken pieces to the pot and stir to coat them with the tomato-onion mixture.

Pour in the orange juice and stir to deglaze the bottom of the pot. Add the marinara sauce, mustard, orange zest, and bay leaf. Stir everything together and reduce the heat to low.

Cover the pot partially and let it simmer gently for 20 to 25 minutes, stirring occasionally. During the last 3 to 5 minutes of cooking, add the drained canned mushrooms and mix well so they heat through without losing their texture. The chicken will be fully cooked, and the sauce will have thickened naturally. If you prefer a thicker sauce, you can dissolve 1 teaspoon of cornstarch in 1/4 cup (60 ml) of chicken broth and add it at this stage.

Remove the bay leaf, adjust salt and pepper to taste, and serve hot.