Place all of the ingredients in a jar, seal with a lid, and shake until completely combined. Set aside. You could also put all the ingredients in a food processor (I have a mini one)and combine until smooth; set aside.
Preheat oven to 425°F (200°C). Line a large rimmed sheet pan with foil or parchment paper; set aside.
Place potatoes in a large zip top plastic bag. Add 1 tablespoon of olive oil, ¼ teaspoon salt. Toss gently to coat all of the potatoes evenly with the oil.
Spread potatoes onto prepared baking sheet (save the plastic bag so that you can use it again with the green beans and tomatoes). Roast the potatoes in the oven for 15 minutes, stirring once.
While the potatoes are in the oven, put the beans in a steamer basket and steam over 1 inch of boiling water until crisp-tender, 4 minutes; set aside.
A green bean option: If you prefer to have crispier green beans, steam them for a few minutes longer. And instead of roasting in the oven with the potatoes and tomatoes, just set aside the green beans when they’re steamed and crispy and wait for the potatoes and tomatoes to be ready.
If you do choose to roast the green beans, place the green beans and the tomatoes in the large zip top plastic bag. Add 1 tablespoon of olive oil to the bag, along with ¼ teaspoon salt. Toss gently to coat the green beans and tomatoes in the oil and salt.
After the potatoes have been roasting for 15 minutes, remove the baking sheet from the oven. Use a spatula to gently flip over the potatoes to the other side. Transfer the green beans and the tomatoes onto the baking sheet with the potatoes in a single layer. Keep the green beans and tomatoes on a separate section from the potatoes.
Return the baking sheet to the oven and roast potatoes, green beans, and tomatoes for about 10-15 more minutes (stirring halfway through), or until vegetables are tender. Keep an eye on the potatoes, because very small potatoes will be done in about 20 total minutes, while larger potatoes will need closer to 30 minutes. Roast the potatoes until they are crispy on the outside and soft on the inside.
If you notice the potatoes need more time and the green beans and tomatoes look ready, remove the green beans and tomatoes and place them on a serving dish and let potatoes finish roasting. You don’t want over brown green beans. They should just begin to get a little bit of color.
Meanwhile, drain the tuna and place in a bowl. Drizzle about 2 tablespoons of the dressing and toss to coat.
When the vegetables are ready, remove from the oven and let them cool down a few minutes. I served my salad right on the sheet pan. If you prefer, you could arrange it all on a serving dish.
Add the olives to the vegetables.
Place the tuna in the middle of the vegetables and arrange the sliced hard boiled eggs on top. Drizzle on a little bit of the dressing and serve with the extra dressing on the side. Serve while warm.