This kind of Coleus would fill it up in no time. Could probably need to be watered daily, probably all of my suggestions could.
Coleus (Coleus scutellarioides Stained Glassworksโข Burgundy Wedding Train)
Lantana could be interesting in there.
Plectranthus amboinicus or forsteri.
I can imagine Petunias looking really great in this, but they never really last into the heat where I am.
Chenille plant.
Catharanthus roseus (Vinca.)
