In a pot over low heat, add milk, water, instant coffee, ½ cup of cocoa powder and ½ cup of chocolate chunks. Whisk until melted and combined. Turn off the heat and whisk in the butter until it is fully incorporated. Place it in a heat-safe bowl to cool.
In a bowl, add flour, baking powder, and salt. Whisk together.
In the bowl of the cooled chocolate batter, add in room temperature eggs, brown sugar, white sugar, vanilla extract, and avocado oil. Whisk to combine.
Fold ⅓ of the flour mixture into the chocolate batter until just combined and no flour is showing. Continue adding in the flour and folding until combined. Add in the remaining ¼ cup of chocolate chunks and fold to incorporate.
Using an ice cream scoop, scoop 1 ½-2 scoops of the muffin batter into the parchment paper muffin liners. Top with more chocolate chunks.
Bake at 375F for 24 minutes. After 24 minutes, reduce the temperature to 350F and bake for another 8-10 minutes until a toothpick comes out clean when inserting it into the center of the muffin. Allow it to cool.
In a saucepan over low heat, add heavy cream, chocolate chunks and salt. Whisk until melted and the ganache begins to thicken. Remove from heat and place in a piping bag.
Using a knife, cut a small hole in the middle of each muffin and pipe in the ganache. Enjoy warm!