Answer: Chicken burger with mustard on multigrain bread
Step-by-step explanation:
Multigrain bread is made up of flour as well as grains that provides more nutrition and fibre than normal white bread .Chicken is the major protein component for the body
Mustard sauce or paste is made up mustard seeds which is good the body's metabolism and contains magnesium iron etc nutrient which is beneficial for body.
Other burgers are not beneficial for health as mayonnaise is composed of oil and fats which is unhealthy.White bread is less nutritious than whole grain bread.
Thus, the healthiest burger is chicken burger containing multigrain bread and mustard paste.