To en-grain flavor means sprinkling some black pepper and salt on tomato slices as an enhancement.
As a team black pepper and salt certainly enhance the natural flavor that a tomato provides to our palate then again, a tomato is also fine without the two on it.
Personally, I like both options however, just a little pepper without the salt also works for me since our medical experts suggest that our sodium (salt) be limited in our diets. They say North Americans consume too much sodium already because of all the processed foods eaten therefore caution must be exercised in ingesting more sodium even in small meals like this one.
This is my contribution for WP single word prompt:”Grain”.