Preheat oven to 350 degrees F (176 C) and line an 8x8 inch baking dish with parchment paper.
Add oats, almonds, sea salt, and coconut sugar to a blender and mix on high until a fine meal is achieved, scraping down sides as needed.
Add melted coconut oil (5 Tbsp or 75 ml as original recipe is written // adjust if altering batch size) and pulse to combine. This should form a loose dough when squeezed between two fingers. Add more if it's too dry.
Add chopped pecans and pulse a few more times to combine - you want a little texture here so leave a little chunky.
Transfer mixture to parchment-lined baking sheet and spread evenly. Then place parchment paper on top and use a flat-bottomed object, such as a drinking glass, to press down firmly until it’s evenly distributed and well packed.
Bake for 15 minutes, then increase heat to 375 F (190 C) and bake for 5-10 minutes more, or until the edges are golden brown and there is some browning on the surface. Remove from oven to cool slightly.
In the meantime, add chocolate to a medium mixing bowl. Add almond milk to a separate small mixing bowl or measuring cup and microwave for 30 seconds (or heat in a saucepan until almost boiling). Add milk to chocolate and don’t touch for 5 minutes so it can melt.
Stir gently with a wooden spoon to incorporate. Then add melted coconut oil and cover. Let rest untouched for another 10 minutes to meld.
Use a mixer (or whisk) to beat the mixture together. A few unmelted chocolate pieces are fine. If you prefer sweeter ganache, add powdered sugar at this time (to taste), and whisk/beat to combine. Set aside.
Spread the ganache over slightly cooled crust and sprinkle on a little sea salt for flavor balance (optional). Freeze (or refrigerate) until ganache is no longer wet and slightly firm (or less time if you want gooey, melty chocolate!).
Once the chocolate has set, lift the bars out of the baking dish and gently transfer to a baking sheet (remove parchment paper to avoid burning). Top with halved marshmallows and broil on the top rack on high for 30-45 seconds (watch closely - they can burn quickly!).
Carefully chop into 9 bars (amount as original recipe is written // adjust if altering batch size) and serve immediately. Best when fresh. Store leftovers at room temperature, loosely covered up to 24 hours.
