In a medium bowl, combine the sliced strawberries, blueberries, balsamic vinegar, maple syrup, salt, and pepper. Gently toss to coat the berries and let them marinate for about 10 minutes.
Heat olive oil in a large skillet over medium heat.
Assemble the sandwiches by placing a slice of bread on a clean surface, adding a layer of vegan cheese, followed by a generous spoonful of the marinated berries, and topping with another slice of bread.
Place the assembled sandwich in the skillet and cook for about 3-4 minutes on each side, or until the bread is golden brown and the cheese is melted. You may need to press down gently with a spatula to ensure even cooking.
Once cooked, remove the sandwiches from the skillet and let them cool for a minute. Garnish with fresh basil leaves before slicing in half and serving.