Sear the sea bass in 2 tablespoons of olive oil over medium-high heat until golden and cooked through on both sides, about 8 minutes total. Drain on paper towels and let cool.
Wash and spin-dry the salad greens.
Rinse the cherry tomatoes, pat dry, and quarter them.
Peel and finely chop the onion.
Cut the feta into cubes.
In a large salad bowl, whisk together the vinaigrette ingredients: remaining olive oil, vinegars, mustard, coriander, salt, and pepper. Add the onion, tomatoes, greens, flaked sea bass, feta, and olives.
Gently toss to combine. Refrigerate until serving for the best flavors.
