How do I cut savoriness of a dish?
Savory usually means spicy &amp; salty.

If you wanted to cut the sharp salty taste of the mustard &amp; capers you could have used a 'sweet mustard' preparation.

I'm not sure if the spinach in the 'tuna spinach wrap' was actually leaf spinach or one of those green 'wraps' like a tortilla?
Spinach has a bit of a metallic taste that some people find sharp. 
Switch to a mild lettuce like Romaine or even ice berg to offset such strong flavors as tina, mustard, &amp; capers.

A bland cheese or mayonnaise can also help balance too much sharpness or 'tang' also.