Add oats, diced apples, milk, cinnamon, nutmeg, allspice, and sea salt to a medium saucepan over medium-high heat, stirring until everything is combined. Bring to a boil, then reduce heat to low so that everything simmers for 8-10 minutes, stirring occasionally.
Once done, oats should thicken and become swollen + fluffy and creamy with half the the liquid still remaining. Stir in the condensed milk + maple syrup and let simmer for an additional 1-2 minutes before removing it from heat.
In a medium skillet over medium-high heat, add the butter and heat until melted. Add the brown sugar, cinnamon and sea salt and stir until combined and everything begins to bubble a bit, about 2-3 minutes.
Add the sliced apples and toss until well coated and cook for 8-10 minutes, until tender and the sauce has thickened. Remove from heat.
To serve, portion oatmeal into serving bowl(s) and top with caramelized apples, toasted nuts, and a light drizzle of maple syrup, if desired.
Bon Appetit!
