Slice your red potatoes into 1 inch thick slices. Put them into a large pot of boiling water, and cook for about 20 minutes. Make sure you can easily stab them with a knife before taking them out.
While the potatoes are cooking, put all of the tuna into a bowl and mix with a fork, cutting up the larger chunks of tuna into smaller pieces.
While the potatoes are cooking, you can also make the French dressing. Mix 8 Tbs olive oil, 4 Tbs tarragon vinegar, 2 Tbs dijon mustard, 1 tsp sea salt, 3/4 tsp ground black pepper, 1/2 tsp herbs de provence, and 3 Tbs diced fresh parsley together until a thick dressing forms.
Once the potatoes are cooked, transfer them to a large bowl and cut them into smaller pieces while mixing them up. Do this while they are still warm. You want there to be various sizes of potato in the salad.
Add the tuna to the bowl of potatoes and mix. Then, add the diced white onions and sliced scallions to the bowl and mix.
Lastly, add the French dressing to the bowl and mix.
Serve warm with a side of tomatoes, radishes, pickles or any other veggie of your choice.
You can also refridgerate it and eat it cold later.