There are quite a few Africans, as well as other cichlids, that would do very well in a 55 gallon planted. Africans: Kribensis (Pelvicachromis pulcher) and the rest of the Pelvicachromis group, Buffalo Head/ Block Head (Steatocranus casuarius), possibly Brichardi (Chalinochromis brichardi and the common Neolamprologus brichardi) if there are no other fish as they will take over the tank, and probably any of the Julidochromis group. I have heard of Yellow Labs (Labidochromis caeruleus) in planted tanks as long as a portion of the substrate is left bare. Supposedly they will dig in the bare portion and leave the rest of the substrate and plants alone. I have not heard anything about other Malawi however, and most of the other Malawi are far more aggressive and should be housed only with other Malawi if you learn they may be ok with a bare area and plants.
As far as South Americans, probably ok with plants: Firemouth (Thorichthys meeki), Severum (Heros severus), and any fish of the Geophagus group (these guys are “Earth Eaters” but they act something like cories searching the substrate for bits to eat- they scoop up sand and spit it out, but I still think they’d be fine with plants and they’re very peaceful). S. Americans definitely ok with plants and also pretty peaceful are: Rainbow (Herotilapia multispinosa), Keyhole (Cleithracara maronii), Nicaraguense/ Nicaragua/ Spilotum (Cichlasoma nicaraguense), Dwarf Flag (Laetacara curviceps), Redbreast Acara/ Red Flag (Laetacara dorsigera), Golden Dwarf (Nanacara anomala), Festivum/ Flag Cichlid (Mesonauta festivus and insignis), Checkerboard Cichlid (Crenicara punctulatum), Lyretail Checkerboard Cichlid (Dicrossus filamentosus), Checkerboard Cichlid (Dicrossus masculatus) and of course the Angelfish, Rams, Apistogramma, and Discus.
The small Asian cichlid, the Chromide (Etroplus maculates) is also ok with plants, but it prefers brackish conditions which will limit your plant choices.
I really like cichlids, particularly the more peaceful ones, and have done tons of research on most species because I was asked at work to become the “cichlid expert.” If you have any other cichlid questions I will be happy to try and help you as best I can! I currently have a heavily planted 10 gallon with a pair of Kribensis (Pelvicachromis pulcher) and they are great with the plants and don’t dig at all. If you provide caves such as flower pots or rocks, driftwood, etc, many of the diggers will usually not dig, which would expand the list above to just about all cichlids as long as their tankmates are chosen very carefully. If I had another, larger tank, I would love to try some Buffalo Head and Nigaraguense, both very unusual looking and entertaining fish!