"Gewöhnlich esse ich ein Sandwich."
Übersetzung:Usually I eat a sandwich.
"Ich esse" can be both "I eat" and "I am eating". However, the "usually" doesn't go too well together with "I am eating". "I am eating" means that you are eating right now. This somewhat contradicts the "usually". But if you add some additional information ("At this time, I am usually eating a sandwich") it sounds plausible to me. [Not a native English speaker, though]