In a small bowl, whisk together the olive oil, lemon juice, and dijon mustard, 1/4 tsp. salt and 1/4 tsp. pepper. Grate the garlic into the bowl, add the red onion, stir to combine and let sit for five minutes.
In a large bowl, add the tuna, cannellini beans, olives,pepperoncini, and piquante peppers.
Gently mix to combine. Check seasonings and adjust to suit your taste.