Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the diced onion, carrots, and celery. Sauté for 5-7 minutes until the vegetables soften.
Stir in the minced garlic, grated ginger, and curry powder. Cook for another minute, stirring constantly, until the spices are fragrant.
Pour in the chicken broth and scrape the bottom of the pot to release any browned bits. Add the chicken thighs, rinsed lentils, and rice.
Increase the heat to bring the soup to a boil, then reduce the heat to low. Cover and simmer gently for 20-25 minutes, or until the lentils and rice are tender and the chicken is cooked through.
Remove the chicken thighs from the pot and shred them using two forks. Return the shredded chicken to the soup.
Stir in the fresh spinach and cook for 2-3 minutes until wilted. Remove from heat and stir in the fresh lemon juice. Season with salt and pepper to taste before serving.