Begin by heating the olive oil in a skillet over medium-high heat. Add the diced onions and sauté until they are translucent, about 3-4 minutes.

Add the minced garlic and sliced mushrooms. Cook for an additional 5 minutes until the mushrooms are tender.

Increase the heat to high and add the sliced beef. Season with salt and pepper. Sauté until the beef is browned on the outside but still pink inside, about 3-4 minutes.

Pour in the beef broth, Worcestershire sauce, and Dijon mustard. Stir well to combine. Reduce the heat to medium and simmer for 10 minutes, allowing the sauce to thicken slightly.

Remove the skillet from heat and stir in the sour cream. Mix until fully incorporated and adjust seasoning if needed.

Preheat the oven to 400°F (200°C).

On a baking sheet, arrange the slices of French bread and toast them in the oven for about 5-7 minutes until lightly browned on each side.

Once toasted, remove the bread from the oven and divide the beef stroganoff mixture evenly on top of each slice of French bread.

Sprinkle shredded cheddar cheese over the beef mixture and return to the oven for another 5 minutes, or until the cheese is melted and bubbly.

Remove from the oven and garnish with chopped parsley before serving.