Cook your lentils if they're not already cooked. I like to rinse the lentils well, then cover with cold water so there's a good inch of water over the lentils. Bring to a boil, then reduce the heat to a simmer and set the lid on the pot slightly ajar.
They'll simmer for about 20 minutes, but start checking them at around the15 minutes mark. You want them to be cooked, but still firm - kind of like al dente when making pasta. Drain the lentils and set aside.
Heat the oil in a large heavy-bottomed pan over medium-high heat. Add the onion, and sauté for a couple of minutes until it's just becoming translucent.
Add the carrot, celery, and garlic, and sauté, stirring frequently, until the vegetables have just softened.
Add the cumin, smoked paprika, and chili powder to the pan. Stir the spices through and sauté for 1-2minutes more.
Add the crushed tomatoes, tomato paste, maple syrup, apple cider vinegar, and soy sauce to the pan.
Stir the wet ingredients through and allow the mixture to simmer for about 5minutes, stirring frequently.
Add the drained lentils to the pan, and stir through. Allow the mixture to simmer for another 2-3 minutes with the lentils added.