Begin by patting the chicken fillets dry using a paper towel to help achieve a better sear. Place them in a mixing bowl and season with onion powder, oregano, paprika, salt, and black pepper. Toss well to coat each piece evenly with the spice mixture.

Heat 1 tablespoon of olive oil in a medium skillet over medium-high heat. Arrange the chicken fillets in the skillet and sear until both sides are golden brown and the meat is cooked through, approximately 5 minutes per side, depending on thickness. Once cooked, transfer the chicken to a plate and cover loosely to keep warm.

Add the remaining tablespoon of olive oil to the same skillet. Toss in the sliced mushrooms, season with a pinch of salt and pepper, and cook, stirring occasionally, until they become golden and crisp at the edges.

Reduce the heat slightly, then add the butter and minced garlic to the pan. Sauté for about 1 minute until the garlic is aromatic and the butter is melted and infused with flavor.

Return the chicken fillets to the pan, nestling them among the mushrooms. Spoon some of the garlic butter mixture over the top and sprinkle with chopped fresh parsley. Serve hot alongside cauliflower rice, steamed white rice, or a fresh green salad.