Heat 2 teaspoons olive oil in a sauté pan over medium-high heat. Season the sirloin steak with salt and pepper and cook about 4-5 minutes on the first side. Flip and cook about 4-5 minutes mores.
Remove the steak from the pan and allow it to sit and rest, about 15 minutes.
Meanwhile, reduce the heat to medium and add 2 teaspoons of olive oil to the pan. Add the garlic and onion and cook until softened, about 2 minutes. Add the bell peppers, oregano, and Herbes de Provence and cook until peppers are softened, about 2 minutes more. Season with salt and pepper. Add the red wine and allow it to simmer and reduce, about 2 minutes.
Remove the sautéd vegetables from the heat. Thinly slice the steak against the grain and stir the sliced steak in with the onions and peppers.
In a small saucepan, heat the milk until it is lightly simmering. Add the gorgonzola, stirring until it has fully melted.
Place some of the steak and pepper mixture onto each piece of the toasted baguette. Spoon the cheese sauce over the top. Serve as open-faced sandwiches.