Warm a large saucepan over medium heat and add canola oil.

Swirl the oil to coat the pan.

Add chopped lemongrass, sliced shallot, and sliced ginger to the pan.

Cook, stirring, until fragrant and beginning to soften, about 2 minutes.

Add chicken broth, fish sauce, and brown sugar to the pan.

Bring to a boil, then reduce heat to medium-low and simmer for 10 minutes.

Strain the soup, pressing on solids, and discard solids.

Return the soup to the pan.

Bring back to a simmer over medium-low heat.

Stir in sliced shiitake mushrooms and bell pepper.

Cook for 2 minutes.

Stir in chicken strips and cook until just opaque, about 2 minutes longer.

Stir in coconut milk and lime juice.

Cook, stirring occasionally, until warmed through.

Ladle into serving bowls.

Top with torn cilantro, sliced scallions, and chilies (optional).

Serve with lime wedges.