Cut your tuna into 4-ounce rectangle.
Combine fennel seeds, kosher salt and peppers.
Generously sprinkle tuna all over with the pepper mixture.
In a large skillet over medium high heat, warm the canola oil to a light smoke.
Gently add the tuna to the skillet, reduce the heat slightly and allow to sear undisturbed over medium heat for about 30-45 seconds on each side or until seeds are nicely toasted but not burnt.
When all sides have color add butter to the pan and baste the tuna generously until the butter stops foaming.
Remove loins from pan and slice each one into 5 pieces.
Season slices with additional coarse sea salt.
Combine all ingredients for the vinaigrette except for oil in a blender or Cuisinart.
Finely chop everything in the machine and then reduce to lowest setting.
Slowly incorporate oil until an emulsion is formed and is the consistency of a runny mayonnaise.
Adjust seasoning with salt and Tabasco.
Adjust consistency by mixing in small amounts of oil to thicken or small amounts of vinegar to loosen.
Keep cold and hold covered in the refrigerator for one day.
Combine capers and olives with olive oil fennel seeds, pepper flakes and zest and marinate for up to three days.
In a large bowl combine hearts of romaine with vinaigrette and place on a serving platter.
Scatter marinated capers and olives on top.
Place slices of tuna loin around the salad.
Serve at room temperature.