Roast pepper in the oven for around half an hour until the skin starts to blacken and bubble. Turn the pepper over once or twice during the cooking time
Fry red onion in little oil until caramelised. After around 10 minutes add a splash of balsamic vinegar and set aside
Fry white onion and garlic in a little oil for several minutes until caramelised
Add 2 slices of bread to food processor and pulse until you have crumbs
Put mince in a large mixing bowl and add cooked onion + garlic, mustard, worcestershire sauce & egg and mix until everything is well combined
Add bread crumbs, salt+pepper, rosemary and mix well
Shape mixture into four patties
Add a little oil to frying pan or griddle and cook for a few minutes on each side
Serve burger on toasted buns and top with roasted red pepper, avocado, caramelised onion, tomato and spinach
Recipe by at https://www.caseyjade.com/gourmet-beef-burger/