Preheat a grill or grill pan on medium heat, season both sides of the chicken with a pinch of salt and pepper and cook about 5 - 7 minutes on both sides until it is no longer pink inside and reaches an internal temperature of 160 degrees. (cook time depends on how thick the breast is.) Once cooked thinly slice the chicken.
In a blender or food processor pulse the mayo, basil, and garlic until smooth.
Lightly toast the bread.
Spread the mayo on the bread, place the tomatoes on top and season with salt and pepper; drizzle olive oil over top and layer with arugula, chicken, onion, and fontina cheese. Cut in half and serve with pickles and chips.