To make vinaigrette, place all ingredients in a medium bowl and whisk until creamy.
To make gremolata, heat the oil in a small pan over medium heat. Add breadcrumbs and saute until slightly golden. Let slightly cool and mix in a bowl with parsley and lemon zest.
To make cauliflower, heat grill over medium-high heat and oil grill well.
Remove the outer leaves from cauliflower head. Cut off the bottom stem end slightly so that you create a flat base and can stand the cauliflower up on a cutting board. Resting the cauliflower on the stem, use a large, sharp knife and carefully cut the head into 4 thick or 5 moderate "steaks." . Don't worry if the end pieces fall apart, you can grill them as well.
Carefully brush all sides of cauliflower with oil and season with salt.
Grill cauliflower for 5 to 6 minutes per side or until each side is slightly charred and cauliflower is tender. Remove from the grill and place on serving platter.
Top with capers, drizzle with tahini vinaigrette and finish with a garnish of gremolata.