Heat olive oil in a large pot over medium-high heat. Add diced chicken and cook for 5-6 minutes until browned. Remove chicken and set aside.
In the same pot, add onion, carrots, and celery. Sauté for 5 minutes until softened. Add garlic, ginger, curry powder, and cumin, stirring for 1 minute until fragrant.
Add chicken broth, red lentils, diced apple, and diced tomatoes to the pot. Return chicken to the pot and bring to a boil.
Reduce heat to low and simmer uncovered for 25 minutes until lentils are tender and soup has thickened. Stir in lemon juice, season with salt and pepper, and garnish with fresh cilantro before serving.