Add Classic French Vinaigrette Mix to a mason jar with olive oil and white wine vinegar; shake well. For extra flavor, make a day ahead and store in the fridge up to one week.
Bring a pot of salted water to a boil. Add baby potatoes and cook until fork-tender, about 10 minutes. Remove with a slotted spoon and toss with 1 tablespoon vinaigrette while warm.
Using the same water, blanch green beans for 1-2 minutes until bright green and crisp-tender. Transfer to an ice bath to stop cooking.
In a separate pot, bring water to a gentle boil. Add eggs and cook 7-8 minutes for jammy yolks or 10 minutes for firm yolks. Transfer to an ice bath, peel, and slice in half.
Arrange mixed greens on a large serving platter. Top with potatoes, green beans, cherry tomatoes, tuna, olives, capers, red onion, and eggs.
Drizzle with French vinaigrette, garnish with fresh parsley, and season with salt to taste.