In a small skillet over medium heat, add the olive oil. Once heated, add the onions and cook over medium-low heat until soft and caramelized, stirring occasionally as needed. This will take about 15 to 20 minutes. Once they’re caramelized, add the mushrooms and cook for a further 5 to 7 minutes, until the liquid is released. Add the vegan Worcestershire sauce and cook for one minute more. Remove, season with salt and pepper and set aside.
In the same pan, over medium heat, add the burgers and cook for about 3 to 4 minutes per side.
Place the baguettes onto plates, top with two pieces of romaine lettuce, then the burger. Top with chipotle mayo and sprouts.