Make the mayonnaise by blending the milk and the oil, slowly until it becomes creamy. Then add the remainder of the ingredients, blend some more, add the minced onions, peas and sweet corn, mix to combine and reserve.
Pan sear the vegan burger on both sides, add salt and pepper if needed.
Slice open the bread, spread some vegan mayo, add the mayo and vegetables, add the lettuce, tomatoes, the vegan burger and the cheese. Close it with the other slice of bread.
In a skillet, add some vegan butter, when melted place the cheeseburger upside down to the pan, let it grill for about 5 minutes each side, on medium heat. Flip the cheeseburger, let it grill on the other side as well, turn the heat off, transfer the cheeseburger to plate and serve it with a side of French fries.