In a bowl, combine all the ingredients for the tuna salad. Stir to combine. Taste and season with salt if needed.
To a pan on medium heat, add a drizzle of olive oil. Add 2 oz of feta and place a large slice of sourdough bread on top. Cook for 2 to 3 minutes, until the feta is crispy and golden brown. Flip the slice and transfer to cutting board. Repeat with second slice.
Place the bread feta-side up. To one slice, add the tomatoes, to the other slice, add 3 to 4 scoops of tuna salad. Sandwich the two then cook in olive oil until crispy on both sides, 1 to 2 minutes. Slice and serve.
