Heat olive oil in a Dutch oven over medium-high heat. After 90 seconds when the oil is hot add the whole lion’s mane mushrooms and cook them on all sides for 2-3 minutes until lightly golden all around.
In a cup or small bowl, whisk together the hoisin sauce, sriracha, water, annatto powder, cinnamon, and coriander.
Pour the sauce onto the mushrooms and cook, flipping and pressing the mushrooms down flat with a metal spatula until most of the sauce has caramelized and has been absorbed by the mushrooms.
Remove the mushrooms from the pan, and allow them to cool. Once cool, cut into slices and set aside.
Remove the dried outer leaves from the lemongrass, cut the core of the lemongrass into 4 inch sections and bash them firmly with the side of a cleaver or heavy kitchen knife.
Heat the olive oil in a wide pot or Dutch oven over medium heat. After 90 seconds, when the oil is hot, add the lemongrass and shallots. Cook, stirring regularly, for 5 minutes until the shallots are softened and aromatic.
Add the ginger, annatto powder, 5-spice powder, potatoes, carrots, vegetable stock, rice vinegar, sugar, and salt. Stir to combine. Increase the heat to high and bring the stew to a boil. Reduce to medium-low heat and simmer uncovered for 25 minutes, until the vegetables are tender and the broth has thickened slightly.
Remove and discard the lemongrass stalks. Adjust seasoning with additional salt if needed. Ladle the stew into bowls and garnish with sliced shallots, cilantro, and bird’s eye chilies before serving.