Combine the oats and water in a medium saucepan and bring to a gentle boil over medium heat, with a few bubbles rising around the edges.
Add the peeled and sliced apples, ground cinnamon, ground cardamom, and a pinch of salt to the boiling mixture. Stir to combine and reduce heat to low.
Simmer the mixture gently, stirring occasionally, until the oats are tender and the apples are soft, about 10 minutes. The mixture will start to thicken and become fragrant with cinnamon and cardamom aromas.
Stir in honey or maple syrup if using, to sweeten the oatmeal to your taste. Continue to cook for an additional 1-2 minutes until well incorporated.
Remove from heat and let the oatmeal sit covered for a minute to settle and enhance flavor.
Serve hot, scooping the oatmeal into bowls. The oats should be creamy, with tender apple slices and a warm, aromatic fragrance. Enjoy the comforting aroma and smooth texture.