Heat 1 tablespoon of olive oil in a skillet over medium-high heat. Add the steak and sear for about 4-5 minutes on each side for medium-rare, or until desired doneness. Remove from skillet and let rest for 5 minutes before slicing.

Sauté the Onions and Mushrooms

In the same skillet, add another tablespoon of olive oil. Slice the onion and mushrooms, then add them to the skillet. Sauté for about 5-7 minutes until softened and caramelized. Season with a pinch of salt and pepper.

Pesto

Make the Pesto

In a food processor, combine the basil, arugula, pine nuts, garlic, Parmesan cheese, and salt. Pulse until finely chopped.

Add Olive Oil

With the food processor running, slowly drizzle in the olive oil until the pesto reaches a smooth consistency. Scrape down the sides as needed.

Assembly

Preheat the Oven

Preheat the oven to 350°F (175°C).

Assemble the Sandwich

Slice the baguette in half lengthwise. Spread a generous amount of the basil and arugula pesto on both sides of the baguette.

Add Steak and Vegetables

Layer the sliced steak, grilled onions, and mushrooms on one half of the baguette. Top with cheddar cheese.

Melt the Cheese

Place the assembled baguette in the preheated oven for about 5-7 minutes, or until the cheese is melted and bubbly.

Serve

Remove from the oven, slice into portions, and serve warm.