Yes you can. The texture will not be quite the same  but if mug cakes are your thing, give the microwave method a try. Place the ramekin (one at a time) in the microwave and cook on high for 90 seconds. If the top looks done, insert a toothpick in the middle. If it comes out mostly clean, your baked oats are ready. If not, cook the baked oats longer, in 30-second increments, until the toothpick comes out clean. Note that microwave ovens have different power levels and the cooking time will vary.