Prepare 2 large chicken breasts, by slicing the breasts in half horizontally to create four thinner cuts of chicken.
Whisk together 1 egg and ½ cup heavy whipping cream in a bowl until well combined.
Combine ½ cup all-purpose flour, ½ cup breadcrumbs, 2 teaspoons garlic powder, 1 teaspoon oregano, 1 teaspoon onion powder, 1 teaspoon salt, and ½ teaspoon pepper in a separate bowl.
Next, working with one cutlet at a time, coat the chicken in the egg mixture, and then allow any excess liquid to drip off before moving on to the next step.
Dredge the chicken in the flour mixture, coating it thoroughly on all sides.
Heat 3 tablespoons olive oil in a large skillet over medium-high heat. Sear the chicken for 4-5 minutes on each side. Cook until golden brown and no longer pink. Once the chicken is cooked, remove it from the pan and set it aside.
Gravy
Remove any burnt bits from the bottom of the pan, then add 1 small yellow onion, diced, and 8 ounces sliced mushrooms to the pan. Saute until the onions are translucent and tender. Remove the mushrooms and onions from the pan and set aside.
Reduce the heat to medium and add ¼ cup butter to the pan. Once the butter is melted, gradually whisk in ¼ cup all-purpose flour to create a thick paste. Slowly add 2 cups beef broth and 1 cup heavy whipping cream to the roux, continually whisking as you add.
Once the gravy is smooth and combined, whisk in 1 tablespoon Worcestershire sauce and 1 teaspoon ground mustard, then season with salt and pepper to taste.
Stir in the onions and mushrooms, then add the chicken back to the pan. Coat the chicken in the sauce and serve over mashed potatoes, pasta, or rice.