Make the chipotle jam. Place the chipotle chillies, pasata, garlic, white wine vinegar and brown sugar into a small saucepan over a medium-high heat. Bring to a boil and simmer for half an hour while you make the quesadillas. The leftovers will keep in the fridge in an airtight container for a few weeks.
For the caramelised onions heat a tablespoon of oil over a medium heat and add the onions. Cook for 10 minutes until they are soft then add the vinegar and sugar, cooking for another 5 minutes until they're caramelised. Remove from the heat and tip onto a plate.
Place the pan back on the heat and melt the butter. Add the mushrooms and garlic to the pan and cook for a few minutes until softened. Remove from the heat.
Assemble the quesadillas. Top one tortilla with a quarter of the onions, mushrooms, cheese and rocket. Add another tortilla. Heat a dry pan over a medium-high heat and place the quesadilla carefully into the pan. Cook for a few times and then flip and cook the other side until they're browned. Repeat with the rest of the quesadillas. Serve with the chipotle jam and any other toppings.