Heat the grill for medium high, direct heat.
Arrange the bacon on another rimmed baking sheet and cook over direct heat, covered, until crispy, about 15 minutes. Remove the bacon pan from the grill and set aside.
Grill the halloumi over medium-high direct heat for 2-3 minutes. Set aside to cool for 5 minutes before slicing.
Spread one side of each bread slice with mavo. Lightly toast the buns on the grill while it is still warm, about 2 minutes over medium-high heat. Then coat the untoasted bread side with mayo a build the sandwiches, putting lettuce down first, followed by the cheese, tomatoes, bacon, and finally a second slice of bread. Slice the sandwiches in half and serve.