"Synthesizer" with "food" implies making food out of non-food components. It could be some kind of chemistry lab that's a part of the waste recycling system and that additionally might be somewhat analogous to a super-duper 3D printer that maybe uses nanotechnology but doesn't utilize anything like transporter tech as a principle component.
In that case, something like chicken soup would be easy to make and have look similar to what it usually is- either out of powdered mix with water automatically added and heated (no pouring or stirring), or cooked up out of its chemical formula from scratch. This would explain why the food cubes - that's default food, when the person eating doesn't particularly care what the food is, just wanting to fill their empty stomach and get back to work - Trek's answer to having a protein bar in your back pocket. When they care more, they might ask for a sandwich instead.