Heat a large wok or skillet over medium-high heat and add the oil.
Add the Brussels sprouts and sauté until just fork-tender (about 4 minutes).
Next, add the onions and cook until translucent, then add the garlic and cook for another minute.
Break up any clumps of cold rice, then tip it into the pan, followed by the soy sauce and maple syrup. Cook for about 5 minutes, tossing frequently until the rice is piping hot.