Heat the oven to 350° F.
Line a 12-cup muffin pan with muffin cups.
In a large bowl, whisk the almond flour, arrowroot, cardamom, baking soda and salt.
In a medium bowl, whisk the eggs, honey, orange zest, orange juice and vanilla extract until well blended.
Pour the wet ingredients into the dry ingredients and stir with a spatula until well blended.
Stir in almost all the diced rhubarb.
Scoop heaping ¼-cup scoops into the muffin cups. Distribute any reserved rhubarb on the top of any muffins that look like they need more rhubarb.
Bake for 22-25 minutes, rotating the pan halfway through, until the muffins are golden brown on top and a toothpick inserted into one comes with out with a few crumbs attached but no raw batter (it might get stained from the rhubarb, which is fine).
Let cool completely (on a cooling rack, if using), then enjoy!