Chop the cucumber, bell pepper, and parsley ahead of time. Set aside.
Preheat oven to high broil.
Brush both sides of each baguette slice with butter. Heat a cast-iron skillet over medium heat. Add two tablespoons of olive oil. Toast the baguette slices on both sides until golden. Remove and set aside.
Remove the Angus beef strips from the refrigerator 30 minutes before cooking to allow them to come to room temperature.
Season the beef generously with sea salt and freshly cracked black pepper.
In the same skillet, wipe out breadcrumbs (optional). Add two tablespoons of olive oil and heat over medium-high heat.
Sear the beef strips for about 3 minutes per side, turning once.
Transfer the beef to a plate, cover it loosely, and let it rest for 10 minutes. Slice thinly against the grain to fit each piece of toast.
Arrange toasted baguette slices on a baking sheet.
Top each slice with beef and a combination of Gruyère and Provolone.
Place under the broiler until the cheese is melted and bubbly, about 1–2 minutes.
Remove the bruschetta from the oven and top each one with cucumber, red bell pepper, and parsley.
Drizzle with the remaining two tablespoons of olive oil before serving.
Serve warm as an appetizer or light meal.