2:61
وَإِذْ قُلْتُمْ يَا مُوسَى لَنْ نَصْبِرَ عَلَى طَعَامٍ وَاحِدٍ فَادْعُ لَنَا رَبَّكَ يُخْرِجْ لَنَا مِمَّا تُنْبِتُ الأَرْضُ مِنْ بَقْلِهَا وَقِثَّائِهَا وَفُومِهَا وَعَدَسِهَا وَبَصَلِهَا قَالَ أَتَسْتَبْدِلُونَ الَّذِي هُوَ أَدْنَى بِالَّذِي هُوَ خَيْرٌ اهْبِطُوا مِصْرًا فَإِنَّ لَكُمْ مَا سَأَلْتُمْ وَضُرِبَتْ عَلَيْهِمُ الذِّلَّةُ وَالْمَسْكَنَةُ وَبَاءُوا بِغَضَبٍ مِنَ اللَّهِ ذَلِكَ بِأَنَّهُمْ كَانُوا يَكْفُرُونَ بِآيَاتِ اللَّهِ وَيَقْتُلُونَ النَّبِيِّينَ بِغَيْرِ الْحَقِّ ذَلِكَ بِمَا عَصَوْا وَكَانُوا يَعْتَدُونَ
2:62
إِنَّ الَّذِينَ آمَنُوا وَالَّذِينَ هَادُوا وَالنَّصَارَى وَالصَّابِئِينَ مَنْ آمَنَ بِاللَّهِ وَالْيَوْمِ الآخِرِ وَعَمِلَ صَالِحًا فَلَهُمْ أَجْرُهُمْ عِنْدَ رَبِّهِمْ وَلا خَوْفٌ عَلَيْهِمْ وَلا هُمْ يَحْزَنُونَ
The one food here seems to be metaphorical (Thanks to Arif and Salman for that!) as it does seem to be more fitting into the statement ‘will you substitute what is lower with what is better’. If we take it literally, we don’t even know what the one food is let alone why its better than onions, garlic, cucumbers etc. This is likely to be a biblically influenced mistranslation. The phrase ‘dhuribat alayhim dhillah maskanah’ shows humiliation and stagnation. This does not fit eating onions and garlic!
2/62 corroborates this by showing people responding to this process of 2/61. The amanoo respond to the one ‘food’, the hadoo superficialise it, the nasara assist the process, the sabi’oon are perhaps new entries. These all believe in Allah and the period of outcome.
Quranology Blog 
seems that the garlic and onion are used to change the base flavour/ add to the dish and the cucumber is a garnish – additions/changes in other words, if what has been sent/revealed is not considered to be enough
and the lentils plump it out
That’s a pretty good way of looking at it. I think we should also check the lexicons for other meanings. I am asking an Arab friend now.
I think the key here is higher/lower rather than the specific foods per se. They had manna and salwa sent down to them. These would be the higher, representing Allah’s extra favor and consolation. The garlic and onions are directly from the earth, as they are roots. Cucumbers grow on the ground as they are on vines, and lentils and herbs are low, bushy plants. These plants are physically low, representing the spiritual lowness of the things that they wanted Musa (as) to request. They are a variety of plants, representing variety as well, as what was being objected to was the one food, even though that one was so much better than the variety. I think that using real plants to represent something metaphorical, such as lowliness, is in line with descriptions elsewhere of the plants of paradise, where physical plants, such as date palms and pomegranites are used to represent spiritual fruits.
I am particularly fond of lentils myself, so when I eat them, this can serve as a reminder that no matter how much I enjoy such earthly delights, the spiritual delights found only with Allah are so much better.
I think 2/62 is meant to generalize the lesson and to remind us that even though a specific group, Musa’s people, are being dealt with in the preceding ayaat, these lessons are meant to be taken by all different types of people.