Heat a 10-inch nonstick skillet over medium heat. Melt the butter and swirl the butter in the pan to coat. Add the mushrooms to the pan and season them with salt and pepper. Sauté the mushrooms, stirring occasionally, until the mushrooms are golden brown, about 6 - 8 minutes. Add the minced garlic to the pan, stir and sauté for 30 seconds to 1 minute, or until the garlic becomes fragrant.
While the mushrooms are browning, crack 3 eggs into a bowl and beat them.
Once the mushrooms and garlic are finished, reduce the heat to low-medium.
Pour the beaten eggs into the pan over the mushrooms and garlic. Allow the eggs to set just a little, about 30 seconds to 1 minute, then slightly tilt the pan and use a rubber spatula to lift the edges of the omelet, allowing the uncooked egg to run off and underneath the omelet.
Once the eggs are just set, sprinkle the cheese over the eggs down the center of the omelet and allow to heat for about 30 seconds to 1 minute. Using the rubber spatula, carefully fold one edge of the omelet toward the center, then fold the other edge toward the center, overlapping slightly.
Remove from heat then slide onto a plate. If desired, season with additional salt and pepper and garnish with fresh herbs.