Place the potatoes in a medium saucepot and add enough cold water to cover by at least 2 inches. Add a large handful of salt and bring to a boil over medium heat. Reduce to a simmer and cook until tender and pierces easily when you insert a paring knife, 10 to 15 minutes.
While the potatoes cook, heat a 12-inch nonstick skillet over medium heat. Add the bacon and cook, flipping occasionally, until golden and crispy, 10 to 12 minutes. Remove and let drain on a paper towel-lined plate then cut crosswise 1/4 inch thick. Set aside.
To make the dressing combine the oil, vinegar, both mustards, some pepper and a large
pinch of salt in a small bowl. Whisk together and taste for seasoning.
Once the potatoes have cooked, drain and carefully--they'll be hot--cut in half. Place in a large
bowl and add the bacon. Pour the dressing over the potatoes and bacon and toss. Let sit for a few minutes so the flavors can absorb. Add the chives.
Break the tuna into large chunks directly into the potato salad. Gently toss with a silicone spatula just to mix through, keeping the tuna in large chunks.
Scoop into a shallow bowl or platter, garnish with more chives, black pepper and the chive blossoms, if using. Serve warm.