Heat the oven to 425ºF. Bring a pot of salted water to a boil. Meanwhile:

• Cut the potatoes into ½-inch-thick wedges.
• Trim the stem ends from the green beans.
• Cut the tomatoes into quarters.
• Cut the olives in half.

On a sheet pan, toss the potatoes with 1 teaspoon oil. Season with salt and pepper and roast, turning halfway through, until lightly browned and tender, 12 to 14 minutes. While the potatoes roast, prepare the green beans and eggs.

To the pot of boiling water, add the green beans and cook until crisp-tender, 2 to 3 minutes. Using a slotted spoon, remove the beans from the boiling water; rinse under cold water to stop the cooking.
Carefully lower the eggs into the boiling water. Cook for 5 minutes for soft-boiled, 8 minutes for hard-boiled. Using a slotted spoon, remove them from the hot water, then run under cold water to cool them. Peel carefully. While the eggs cook, prepare the tuna.

• Using the bottom of a bowl, pan, or rolling pin, on a cutting board, lightly crush the coriander seeds. Transfer to a plate.
• Pat the tuna steaks dry with a paper towel. Season generously with salt and pepper. Press each side into the coriander seeds to coat generously.

In a pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the tuna steaks and cook until lightly browned, about 1 minute per side for rare, depending on thickness. Transfer to a plate to rest. Cut the tuna steaks crosswise into ½-inch-thick pieces. While the tuna rests, prepare the dressing and salad.

In a small bowl, combine the mustard vinaigrette base with 1 tablespoon oil. Season to taste with salt and pepper.
In a large bowl, combine the mixed greens, green beans, potatoes, tomatoes, and olives. Add as much of the mustard vinaigrette as you like and toss to coat. Season to taste with more salt and pepper, if needed.

Transfer the salad to individual plates and top with the tuna slices. Cut the eggs in half, arrange them on top, and serve.