As a perimeter supermarket shopper I can't think of many 2 ingredient meals that follows our eating habits but this is what comes to mind as fast, healthful and can be cooked in one pot:
dried or frozen tortellini and spinach or kale soup - 3 ingredients
wonton soup w/ veggies -3 ingredients
rice cooked with chicken broth and veggies in 1 pot -3 ingredients
ratatouille served over rice or noodles - 2 ingredients; we always keep "rata" in the freezer and it also works nicely as an omelet filling for a 3 ingredient meal.
P+J sandwich - 3 ingredients. Only hot if you toast the bread;).