Turn on the grill if makeing on the grill. Or turn on a grill pan over medium heat and the oven to 150 degrees.
Brush the chicken filets with olive oil and season with sea salt. Put on the grill or in the grill pan.
Grill on the grill for 8-10 minutes (until it reaches about 72 degrees Celcius). Or fry in a grill pan for 2-3 minutes on each side and then put in an oven safe baking dish and bake for 12-18 minutes.
When 2-3 minutes remain of the cooking time for the chicken add the sliced tomatoes and peaches on the grill/frying pan and grill/fry for about 1 minute on each side. They should just get warm but not soggy and cooked though.
Place the chicken breast fillet on a cutting board and slice.
Place on two plates and divide the tomatoes and peaches equally between two plates.
Serve with some thick balsamic vinegar if desired.