Preheat oven to 350°F (180°C).
In a med bowl prepare the rub by mixing the chopped mint, rosemary, salt, pepper, garlic, Dijon mustard and lemon juice and set aside.
Use a 9 x 13 baking dish in which to combine the chopped onions, apples, bay leaves and port. Place the roast on top of the bed of apples and onions. Take the mustard rub and massage it into the roast, getting it into all the crevices, be generous and use the entire rub.
Place the roast into the oven for 2 hours until it is golden brown and has reached an internal temperature of 165 degrees.
Remove the roast from the pan and let rest for 10 to 15 minutes on a cutting board, meanwhile use a potato masher to mash the apples and onions, making a compote, serve alone side the roast.