For the burger, place the steak, onion, garlic and chilli in a food processor and pulse until minced. Season with salt and freshly ground black pepper and shape into a patty.
Dredge the burger in the flour. Heat one tablespoon of the olive oil in a non-stick frying pan and fry the burger for 3-4 minutes, or until cooked through.
Drizzle the cut sides of the baguette with the remaining oil and fry, oiled-side down, until lightly toasted, pressing down with a spatula if necessary.
For the relish, heat the oil in a small saucepan and fry the pepper and chilli together for 2-3 minutes, or until the pepper starts to soften.
Add the remaining ingredients and simmer for 4-5 minutes.
To serve, place the burger inside the baguette, sprinkle with cheese and top with a dollop of relish.