Preheat the oven to 350 degrees Fahrenheit. Line a 12-cup muffin tin with paper liners.
To make the streusel topping: In a medium bowl, combine the oats, sugar, baking soda, cinnamon, and salt. Add the solid coconut oil and cut or pinch it into the dry ingredients until you have pea-size chunks. Set aside.
To make the muffins: In a small bowl, combine the coconut milk and vinegar and set aside.
In a large bowl, combine the flour, oats, sugar, baking powder, baking soda, psyllium husk powder (if using), and salt. Add the applesauce, coconut oil, and coconut milk mixture and stir until well combined. It will be a very fluffy batter. Very gently fold in the raspberries.
Scoop the batter into the prepared muffin tin and spoon the streusel evenly over the batter. Bake for about 25 minutes, until golden and puffed up. Let cool in the tin for a few minutes before serving warm or at room temperature.