Mix the oats with 200ml of warm water in a large mixing bowl. If using oats that are more whole and less broken up, add another 50ml of water (~1/4cup). Let this sit for an hour to soften the oats. You can also use about 350-400 grams of leftover oatmeal in this step instead.
Add to the oat mixture: the additional 150ml of water, yeast, flour, and salt. Mix together (we just use a spoon) until it forms a cohesive ball of dough. If it's super dry and not coming together, add a little bit more water. If it seems super wet, add a little bit more flour.
Let this sit for an hour and a half. Every 20 minutes during this time, complete a "stretch and fold" of the dough. Basically, with slightly damp hands (just run them under water briefly) you will pull up the sides of the dough in the bowl and fold them inwards, along four quadrants of the bowl. See this great blog post from The Clever Carrot for more help with this technique! Try to complete three "stretch and folds" during the rising time; then the dough will rest for the last 20-30 minutes. After the last stretch and fold, preheat your convection/fan oven to 375F or 190C. Place a roasting dish or a deep baking sheet on the bottom rack of the oven or just on the bottom of the oven and let it preheat with the oven.
Right before shaping the rolls, put some water (we use around 200-300ml) in a kettle and bring to a boil - you'll need this when the rolls are ready to bake.
Once the dough is ready, prepare a baking sheet with parchment paper or a silicone baking mat. We place all the rolls on one baking sheet, but you can separate them onto two baking sheets if you have the space in the oven for them!
To shape the rolls: scoop up the dough with a wet spoon and place it on the baking sheet. You can use the spoon to make the rolls a little rounder once they're on the baking sheet.
Optional step - once the rolls are all placed on the baking sheet, take a sharp knife dipped in water and score each roll across the top.
Let the rolls rest for around 10 minutes after shaping and before putting them in the oven.
Place the rolls in the preheated oven, then very carefully pour the boiling water into the roasting dish/deep baking sheet in the bottom of the oven. This will make a lot of sound and may splash a little, so be careful! Quickly close the oven door to trap the steam.
Bake the rolls for 25-30 minutes, until golden and hollow-sounding when you tap them. This time may vary slightly for your oven, so keep an eye on them.
Enjoy! We love to eat these slightly warm from the oven with butter and jam.