Preheat oven to 350F. Line a loaf pan with parchment paper and set aside.
Place lentils and vegetable broth in a large pan and bring to a boil. Cover and simmer for 10 minutes, or until lentils are soft.
In another pan over medium heat, add a couple tablespoons of water and cook with celery, onions, garlic, and mushrooms until softened, adding more water as necessary to prevent sticking. Add the sage, rosemary, thyme, salt, tamari, and kale and cook until kale is wilted, about 2-3 minutes. Set aside to cool slightly.
When lentils are done cooking, pulse them in a food processor until smooth. Add the mushroom and kale mixture, oats and spinach and pulse until thoroughly combined.
Scrape the lentil mixture into the prepared loaf pan and smooth the top. Lightly spread the ketchup over the top with a spoon.
Bake for 35-40 minutes, or until the lentil loaf starts to lift away from the sides and the top starts to brown. Allow to cool for a few minutes, then slice and enjoy!