Spicy Thai Coconut Chicken Soup

Heat a Dutch oven over medium heat. Add oil to pan; swirl to coat. Add mushrooms and the next 4 ingredients (through lemongrass); cook 3 minutes, stirring occasionally. Add chile paste; cook 1 minute. Add Chicken Stock, coconut milk, fish sauce, and sugar; bring to a simmer. Reduce heat to low; simmer for 10 minutes. Add chicken to pan; cook 1 minute or until thoroughly heated. Discard lemongrass. Top with onions, cilantro, and juice.