To make it easier, I recommend buying already sliced mushrooms. They also tend to cost the same as whole!

If you bought whole mushrooms, use a damp cloth (or paper towel) to gently rub off any dirt then slice. Medium to thick slices will work best.

Cut off the ends of the onion then peel. Cut in half and then into half moon slices.

Wash and discard any hard outer layers of the fennel then thinly slice.

I recommend using a cast iron or stainless steel skillet for this.

Add 2 tablespoons of olive oil to your large skillet and heat on high heat.

Once the skillet is hot (should taken about 1 minute), lower the heat to medium add the sliced onion and sauté for 5-7 minutes.

Next, add the sliced fennel and and sauté for 15-20 minutes or until lightly golden and caramelized.

Season with 1/2 teaspoon of salt, stir then move to a bowl.

Use this skillet again for the next step. No need to clean.

To your dirty skillet, add 1 tablespoon of olive oil and turn the heat back up to high.

Add the sliced mushrooms and using your spoon, spread out into one even layer.

It will appear to be a lot of mushrooms but as they cook, they will shrink down tremendously.

Now, lower the heat to medium and allow the mushrooms to sauté and caramelize undisturbed for 10 minutes.

This means no stirring, no touching for 10 minutes!

It will seem hard but just set a 10 minute timer and scroll through instagram while you patiently wait for the mushrooms get nice a brown.

Once the timer goes off, stir the mushrooms and sauté for another 10 minutes or until the mushrooms are evenly browned and border line burnt!

If you have the Mushroom Multipurpose UMAMI seasoning, now is a great time to use it.

Add 1 teaspoon of salt and 1 teaspoon of the UMAMI seasoning to the mushrooms, stir then turn off the heat.

If you do not have the seasoning, simply add 1 teaspoon of salt and 1/4 teaspoon of black pepper.

Next, add 2 tablespoons of mascarpone cheese and 2 tablespoons of grated parmesan cheese to the mushrooms with the heat off.

Stir until the cheeses are fully melted and evenly incorporated with the mushrooms.

Using your wooden spoon or spatula, divide the mushroom mixture into two halves and form them into an oval shape.

Place two slices of the provolone cheese onto each of the mushroom mixture halves (four slices in total), turn the heat to medium-low and cover the skillet with a lid so that cheese can melt. Check on it after 3-5 minutes to see if the cheese is fully melted.

While the provolone cheese melts, toast your hoagie rolls on both sides in a second large skillet with a bit of olive oil on medium-high heat.

Add a bit of arugula to the bottom halves of the toasted hoagie rolls then top with the caramelized onion and fennel.

Next, using a spatula, carefully lift the mushroom mixture with the melted provolone cheese and place them on top of the arugula and caramelized onion and fennel.

Add the top halves of the toasted hoagie rolls and enjoy!