Heat a small amount of plant-based butter in a pan on medium heat. Add the chopped garlic and soften for a minute, followed by the spinach and a pinch of salt. Cook gently until all the spinach has wilted down, then remove from the pan and set aside.
In a bowl, use a fork to break up the pre-cooked/leftover haggis and make it easier to work with.
Take two slices of bread and butter one side of each. Place the buttered side of one slice face down on a board, then layer on half of the spinach, haggis, and cheese. Add a few dashes of vegan Worcestershire sauce and then place the other slice of bread on top (buttered side facing up). Use a spatula to press down firmly on the sandwich.
Using the same pan as before, heat this on medium heat and place the sandwich in the pan. Cook for three minutes or until golden underneath, pressing down firmly with a spatula.
Once the underside has turned golden and crispy, flip the toastie over carefully and repeat on the other side. Cook until both sides are golden and the cheese has started to melt, turning down the heat slightly if necessary.
Repeat this process for the other toastie, then slice in half and serve warm with fresh spinach, salad leaves, or as it is.