Place 1 tablespoon of the olive oil and 1 tablespoon of the unsalted butter in a sauté pan over medium heat. Add the chicken tenderloins once the butter is melted.
Season generously the chicken tenderloins with the garlic powder, lemon pepper seasoning, and pepper. Brown each side for about 5-7 minutes. Once each side has been browned, add ¼ cup of water and ¼ cup of the parsley into the sauté pan and put the lid on. Let the chicken simmer in the pan for about 6-7 minutes.
Remove the chicken from the pan and set it aside. Add ¼ cup water to the pan to remove the browned bits at the bottom. (This is where all the flavor is!) Optional: Add your mushrooms to the water and season with salt and pepper depending on preference. Cook until lightly browned as this will continue cooking with the garlic in the next step.
Adjust the temperature to medium-low heat and add the remaining tablespoon of olive oil and unsalted butter to the sauté pan. Once the butter is melted, place the garlic cloves into the pan. Cook for 5-7 minutes until lightly browned or until fully cooked. (The garlic cloves will be combined with the mushrooms previously added).
Stir in the heavy cream and lemon juice. Cook for another 5 minutes. The sauce will thicken and change into a beautiful brownish color. Add the remaining ½ cup of parsley and season the sauce with salt and pepper depending on preference.
Reduce the heat to low and put the chicken tenderloins back into the pan. Combine with sauce and let it warm for about 1-2 minutes in the sauté pan.
Plate the chicken tenderloins and sauce with additional lemon juice and pepper if desired.