Slicing the beets thinly, and roasting them this way, not only cuts down cooking time, but also makes the beets taste even better — slightly crispy on the outside, but still chewy on the inside.
Approximately 3 medium beets, peeled, and thinly sliced into whatever shape / size you desire to sit nicely atop their rice bases (I halved them lengthwise, placed the flat side down, and then thinly sliced them).